vim/c: added vim setup and c language setup

- added vim setup
- added vim autocomplete guide based on coc
- added c support by coc lsp
- added c setup

wiki/linux/vim/coc.md

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+# Coc
+
+[Conquer of completion](https://github.com/neoclide/coc.nvim) enables full
+language server protocol support for neovim.
+It is written specifically for neovim.
+
+The coc config file is located in `.config/nvim/coc-settings.json`.
+
+## Installation
+
+- Install `nodejs`
+- Install [vim-plug](vim-plug.md)
+- Add coc.vim to your init.vim
+  - Add `Plug 'neoclide/coc.nvim', {'do': 'yarn install --frozen-lockfile'}`
+  to your Plug-Section
+
+## Base config
+
+Add the base configuration to your vim config file.
+
+```vimscript
+" neoclide/coc.nvim
+inoremap <silent><expr> <TAB>
+      \ pumvisible() ? "\<C-n>" :
+      \ <SID>check_back_space() ? "\<TAB>" :
+      \ coc#refresh()
+inoremap <expr><S-TAB> pumvisible() ? "\<C-p>" : "\<C-h>"
+
+function! s:check_back_space() abort
+  let col = col('.') - 1
+  return !col || getline('.')[col - 1]  =~# '\s'
+endfunction
+
+if has('nvim')
+  inoremap <silent><expr> <c-space> coc#refresh()
+else
+  inoremap <silent><expr> <c-@> coc#refresh()
+endif
+
+inoremap <silent><expr> <cr> pumvisible() ? coc#_select_confirm()
+                              \: "\<C-g>u\<CR>\<c-r>=coc#on_enter()\<CR>"
+
+nmap <silent> gd <Plug>(coc-definition)
+nmap <silent> gy <Plug>(coc-type-definition)
+nmap <silent> gi <Plug>(coc-implementation)
+nmap <silent> gr <Plug>(coc-references)
+nnoremap <silent> K :call <SID>show_documentation()<CR>
+
+function! s:show_documentation()
+  if (index(['vim','help'], &filetype) >= 0)
+    execute 'h '.expand('<cword>')
+  elseif (coc#rpc#ready())
+    call CocActionAsync('doHover')
+  else
+    execute '!' . &keywordprg . " " . expand('<cword>')
+  endif
+endfunction
+
+autocmd CursorHold * silent call CocActionAsync('highlight')
+
+nmap <F5> <Plug>(coc-rename)
+
+xmap <leader>f  <Plug>(coc-format-selected)
+nmap <leader>f  <Plug>(coc-format-selected)
+
+augroup mygroup
+  autocmd!
+  autocmd FileType typescript,json setl formatexpr=CocAction('formatSelected')
+  autocmd User CocJumpPlaceholder call CocActionAsync('showSignatureHelp')
+augroup end
+```
+
+## Extensions
+
+Extensions can be added to the vim config aswell.
+A basic example for adding a few extensions is:
+
+```vimscript
+let g:coc_global_extensions = [
+    \ 'coc-java',
+    \ 'coc-markdownlint',
+    \ 'coc-python',
+    \ 'coc-sh',
+    \ 'coc-vimtex',
+    \ ]
+```
+