[WIP] an option to disable rich documentation

[randy3k]

it is needed for editor with less fancy markdown renderer.

Shall we actually turn it off as default and only provide the rich markdown if client to specify via
MarkdownClientCapabilities? I imagine vscode-r-lsp could enable it by default.

[randy3k]

Actually, now I am thinking that we should less depend on settings via .Rprofile but utilizing the workspace/didChangeConfiguration. So ignore this PR for now, I will come back with a better solution.

[randy3k]

We have the following settings

languageserver.snippet_support
languageserver.max_completions
languageserver.lint_cache
languageserver.formatting_style
languageserver.server_capabilities
languageserver.link_file_size_limit

I think we should find a way to consistently expose them to workspace/didChangeConfiguration as well as via options from .Rprofile.

[randy3k]

closed in flavor of #439