Add [O, ]O and cO map groups to change all windows

The `s:windo` wrapper is based on
https://github.com/vim-scripts/ArgsAndMore/blob/848dec40e4d23fa3124c83009512eb5a22bd36b8/autoload/ArgsAndMore.vim#L127-L138.

plugin/unimpaired.vim

@@ -208,10 +208,29 @@ function! s:toggle(op) abort
   return eval('&'.a:op) ? 'no'.a:op : a:op
 endfunction
 
+function! s:windo(command)
+  " By entering a window, its height is potentially increased from 0 to 1 (the
+  " minimum for the current window). To avoid any modification, save the
+  " window sizes and restore them after visiting all windows.
+  let winrestcmd = winrestcmd()
+  let currwin = winnr()
+  let prevwin = winnr('#') ? winnr('#') : 1
+  echom a:command
+  execute 'windo '.a:command
+  execute prevwin.'wincmd w'
+  execute currwin.'wincmd w'
+  silent! execute winrestcmd
+endfunction
+
 function! s:option_map(letter, option, mode) abort
   exe 'nnoremap [o'.a:letter ':'.a:mode.' '.a:option.'<C-R>=<SID>statusbump()<CR><CR>'
   exe 'nnoremap ]o'.a:letter ':'.a:mode.' no'.a:option.'<C-R>=<SID>statusbump()<CR><CR>'
   exe 'nnoremap co'.a:letter ':'.a:mode.' <C-R>=<SID>toggle("'.a:option.'")<CR><CR>'
+
+  exe 'nnoremap [O'.a:letter.' :call <SID>windo('''.a:mode.' '.a:option.''')<CR><C-R>=<SID>statusbump()<CR><CR>'
+  exe 'nnoremap ]O'.a:letter.' :call <SID>windo('''.a:mode.' no'.a:option.''')<CR><C-R>=<SID>statusbump()<CR><CR>'
+  " XXX: uses the value of the current window to toggle all.
+  exe 'nnoremap cO'.a:letter.' :call <SID>windo('''.a:mode.' <C-R>=<SID>toggle("'.a:option.'")<CR>'')'
 endfunction
 
 nnoremap [ob :set background=light<CR>