vim:autocmd: Use matchadd to Highlight cword

Use `matchadd` instead of `match` as it has no limit on the number of
highlights.

Also call the function every time the cursor moved instead of only when
holding. This makes it snappier while also keeping the highlight when
moving inside the cword.

.config/vim/vimrc.d/80-autocommands.vim

@@ -53,14 +53,18 @@ augroup END
 
 " Highlight word under cursor
 function! HighlightCurrentWord()
+	if exists('w:cword_match_id')
+		call matchdelete(w:cword_match_id)
+		unlet w:cword_match_id
+	endif
 	if (expand('<cword>') != '')
-		exec 'match CursorColumn /\V\<' . escape(expand('<cword>'), '/\') . '\>/'
+		let w:cword_match_id = matchadd('CursorColumn',
+			\ '\V\<' . escape(expand('<cword>'), '/\') . '\>')
 	endif
 endfunction
 augroup highlight_current_word
 	au!
-	au CursorHold * call HighlightCurrentWord()
-	au CursorMoved * match
+	au CursorMoved * call HighlightCurrentWord()
 augroup END
 
 " Do not mark input from stdin as modified