refactor!: extract mason-lspconfig to separate plugin (#109)

The rationale behind this is to make boundaries clearer as mason.nvim
has no direct relation with lspconfig per se.

Also, hopefully, by having it as a separate package like this would
encourage more people to write similar extensions (think mason-dap and
mason-null-ls). Ideally such extensions wouldn't be required at all, but
there are definitely gaps to fill as of today.

From now on you'll need to add `williamboman/mason-lspconfig.nvim` as
a plugin if you want to use the `mason-lspconfig` extension:

```lua
use {
    { "williamboman/mason.nvim", branch = "alpha" },
    "williamboman/mason-lspconfig.nvim",
    "neovim/nvim-lspconfig",
}
```

```lua
Plug "williamboman/mason.nvim", { 'branch': 'alpha' }
Plug "williamboman/mason-lspconfig.nvim"
Plug "neovim/nvim-lspconfig"
```

2 files changed, 0 insertions, 221 deletions

diff --git a/doc/mason-lspconfig.txt b/doc/mason-lspconfig.txt
deleted file mode 100644
index 052c57ca..00000000
--- a/doc/mason-lspconfig.txt
+++ /dev/null
@@ -1,206 +0,0 @@
-*mason-lspconfig*
-
-Minimum version of neovim: 0.7.0
-
-Author: William Boman
-
-==============================================================================
-INTRODUCTION                                    *mason-lspconfig-introduction*
-
-`mason-lspconfig` is a native extension to `mason.nvim` that ships with
-`mason.nvim`. It bridges `mason.nvim` with the `lspconfig` plugin in order to
-make it easier to use the both plugins together.
-
-It is recommended to use this extension if you use `lspconfig`.
-
-Among other things, it provides convenience APIs that allow you to use
-mason.nvim as the main control for dynamically setting up installed servers on
-an ad-hoc basis. It also provides extra commands such as `:LspInstall` that
-for example allow you to install servers for the current 'filetype'. Lastly,
-it also registers a setup hook with `lspconfig` that ensures servers installed
-with `mason.nvim` are set up with the necessary extra configuration (however,
-this only applies to a few select servers!).
-
-`lspconfig`: https://github.com/neovim/nvim-lspconfig
-
-==============================================================================
-REQUIREMENTS                                    *mason-lspconfig-requirements*
-
-`mason-lspconfig` requires `lspconfig` to be installed. Note that `lspconfig`
-needs to be available when setting up `mason-lspconfig` - so if you lazy load
-either plugin make sure `lspconfig` is not loaded after `mason-lspconfig`.
-
-Also, make sure not to set up any servers via `lspconfig` _before_ calling
-`mason-lspconfig`'s setup function.
-
-==============================================================================
-QUICK START                                       *mason-lspconfig-quickstart*
-
-The only thing needed to enable the `mason-lspconfig` plugin is to make sure
-to call the `setup()` function:
-
-    require("mason").setup()
-    require("mason-lspconfig").setup()
-
-==============================================================================
-COMMANDS                                            *mason-lspconfig-commands*
-
-                                                                 *:LspInstall*
-:LspInstall [<server>...]
-
-Installs the provided servers. This command only accepts servers that have a
-corresponding server configuration in `lspconfig`.
-
-You may also provide a language, like `:LspInstall typescript`. This will
-prompt you with a selection of all available servers for that given language.
-
-When the command is ran without any arguments, the currently active buffer's
-'filetype' will be used to identify relevant servers, and you will be prompted
-with a selection of all suggested servers.
-
-                                                               *:LspUninstall*
-:LspUninstall <server> ...
-
-Uninstalls the provided servers.
-
-==============================================================================
-SETTINGS                                            *mason-lspconfig-settings*
-
-You can configure certain behavior of `mason-lspconfig` when calling the
-`.setup()` function.
-
-Refer to |mason-lspconfig-default-settings| for all available settings.
-
-Example:
-
-    require("mason-lspconfig").setup({
-        ensure_installed = { "rust_analyzer", "tsserver" }
-    })
-
-                                            *mason-lspconfig-default-settings*
-
-    local DEFAULT_SETTINGS = {
-        -- A list of servers to automatically install if they're not already installed. Example: { "rust-analyzer@nightly", "sumneko_lua" }
-        -- This setting has no relation with the `automatic_installation` setting.
-        ensure_installed = {},
-
-        -- Whether servers that are set up (via lspconfig) should be automatically installed if they're not already installed.
-        -- This setting has no relation with the `ensure_installed` setting.
-        -- Can either be:
-        --   - false: Servers are not automatically installed.
-        --   - true: All servers set up via lspconfig are automatically installed.
-        --   - { exclude: string[] }: All servers set up via lspconfig, except the ones provided in the list, are automatically installed.
-        --       Example: automatic_installation = { exclude = { "rust_analyzer", "solargraph" } }
-        automatic_installation = false,
-    }
-
-==============================================================================
-DYNAMIC SERVER SETUP                    *mason-lspconfig-dynamic-server-setup*
-
-`mason-lspconfig` provides extra opt-in functionality that allow you to set up
-LSP servers installed with `mason.nvim` without having to manually edit your
-Neovim configuration for every single server you want to use. This is also
-convenient if you want to use `mason.nvim` as the main control mechanism for
-which servers to set up. It also makes it possible to use newly installed
-servers without having to restart Neovim! Example:
-
-    require("mason").setup()
-    require("mason-lspconfig").setup()
-    require("mason-lspconfig").setup_handlers {
-        -- The first entry (without a key) will be the default handler
-        -- and will be called for each installed server that doesn't have
-        -- a dedicated handler.
-        function (server_name) -- default handler (optional)
-            require("lspconfig")[server_name].setup {}
-        end,
-        -- Next, you can provide targeted overrides for specific servers.
-        -- For example, a handler override for the `rust_analyzer`:
-        ["rust_analyzer"] = function ()
-            require("rust-tools").setup {}
-        end
-    }
-
-Refer to |mason-lspconfig.setup_handlers()| for more information.
-
-==============================================================================
-Lua module: mason-lspconfig
-
-                                                     *mason-lspconfig.setup()*
-setup({config})
-    Sets up mason with the provided {config} (see |mason-lspconfig-settings|).
-
-                                            *mason-lspconfig.setup_handlers()*
-setup_handlers({handlers})
-    Advanced feature ~
-        This is an advanced, opt-in, feature that require some careful reading
-        of the documentation.
-
-        The recommended method to set up servers with lspconfig is to do so by
-        following their guides, see |lspconfig-quickstart|.
-
-    Registers the provided {handlers}, to be called by mason when an installed
-    server supported by lspconfig is ready to be setup.
-
-    {handlers} is a table where the keys are the name of an lspconfig server,
-    and the values are the function to be called when that server is ready to
-    be set up (i.e. is installed).
-
-    You may also pass a default handler that will be called when no dedicated
-    handler is provided. This is done by providing a function without a key
-    (see example below).
-
-   NOTE: ~
-       The server names provided as keys are the lspconfig server names, not
-       mason's package names, so for example instead of "lua-language-server"
-       it's "sumneko_lua".
-
-    Example: ~
-
-        require("mason-lspconfig").setup_handlers({
-            -- The first entry (without a key) will be the default handler
-            -- and will be called for each installed server that doesn't have
-            -- a dedicated handler.
-            function (server_name) -- default handler (optional)
-                require("lspconfig")[server_name].setup {}
-            end,
-            -- Next, you can provide targeted overrides for specific servers.
-            ["rust_analyzer"] = function ()
-                require("rust-tools").setup {}
-            end,
-            ["sumneko_lua"] = function ()
-                lspconfig.sumneko_lua.setup {
-                    settings = {
-                        Lua = {
-                            diagnostics = {
-                                globals = { "vim" }
-                            }
-                        }
-                    }
-                }
-            end,
-        })
-
-    See also: ~
-        You may achieve similar behaviour by manually looping through the
-        installed servers (see |mason-lspconfig.get_installed_servers()|) and
-        setting each one up.
-
-                                     *mason-lspconfig.get_installed_servers()*
-get_installed_servers()
-    Returns the installed LSP servers supported by lspconfig.
-
-    Note that the strings returned are the lspconfig server names, not the
-    mason package names. For example, "sumneko_lua" is returned instead of
-    "lua-language-server". This is useful if you want to loop through the
-    table and use its values to directly interact with lspconfig (for example
-    setting up all installed servers).
-
-    Returns: ~
-        string[]
-
-    See also: ~
-        |mason-registry.get_installed_packages()|
-        |mason-registry.get_installed_package_names()|
-
-
- vim:tw=78:ft=help:norl:expandtab:sw=4
diff --git a/doc/mason.txt b/doc/mason.txt
index 20773a2a..8dcb242a 100644
--- a/doc/mason.txt
+++ b/doc/mason.txt
@@ -22,21 +22,6 @@ API reference: ~
     https://github.com/williamboman/mason.nvim/blob/alpha/doc/reference.md
 
 ==============================================================================
-EXTENSIONS                                                  *mason-extensions*
-
-
-                                                  *mason-extensions-lspconfig*
-`mason-lspconfig` is a native extension to `mason.nvim` that ships with
-`mason.nvim`. It bridges `mason.nvim` with the `lspconfig` plugin in order to
-make it easier to use the both plugins together.
-
-It is recommended to use this extension if you use `lspconfig`. To use this
-extension, make sure to set it up after `mason.nvim`, like so:
-
-    require("mason").setup()
-    require("mason-lspconfig").setup()
-
-==============================================================================
 REQUIREMENTS                                              *mason-requirements*
 
 `mason.nvim` relaxes the minimum requirements by attempting multiple different