Support connecting servers using sockets

[techee]

The plugin currently only works over stdin/stdout and takes over the responsibility for starting and stopping LSP servers. Some LSP servers, such as Godot, have to run all the time because they provide other functionality and have to be connected using sockets - this is not supported by the server at the moment.

[techee]

This is now supported using https://github.com/techee/lsp-proxy and I don't plan this feature directly in the plugin any more.