supporting kind information to auto-complete for LSP like output

[akh2008]

Parse the additional info for autocompletion, so that pop-up window can display the detail as help and Kind info like Function, struct, property, macro, method etc similar to LSP. The enhanced omnicompletion is inspired from coq.thirdparty omnicompletion.

Autocompletion after the fix.

Prior to fix:

[RaafatTurki]

I've done a hacky little thing in the cmp format function to improve omnifunc a bit

before:

after:

format = function(entry, vim_item)
  if entry.source.name == 'omni' then
    if entry.completion_item.documentation == nil then
      entry.completion_item.documentation = vim_item.menu
      vim_item.menu = nil
    end
    vim_item.kind = 'Ω'
    vim_item.kind_hl_group = 'CmpItemKindProperty'
  else
    -- set vim_item.kind to an lsp related icon depending on vim_item.kind
  end

  return vim_item
end

[hrsh7th]

Out of curiosity, why not use the cmp-nvim-lsp sources?

[hrsh7th]

I think this function does not support string[] and { word: string}[] forms.

What omnifunc did you test with?
I think the error occurs in omnifunc outside the test scope.

[wookayin]

I think this feature can be useful for treesitter omnifunc completion (try :PreviewQuery). It requires some rebase and fix applied, such as #6 (01f0f66). @akh2008 Would you want to work on rebasing and wraping it up? I can help and provide some reviews.