vim:keys: Add <leader>utc to convert unix time

Add `<leader>utc` to convert unix timestamps into a human readable
format.

.config/vim/vimrc.d/40-keys.vim

@@ -200,3 +200,8 @@ xnoremap gm :Man <C-r><C-a><CR>
 
 " Format the current paragraph
 nmap Q gqap
+
+" Convert Unix timestamp to human readable
+" Mnemonic: "Unix timestamp convert" with pun to UTC
+nnoremap <leader>utc ciw<C-r>=strftime("%c", @")<CR><Esc>
+vnoremap <leader>utc :s/\v(^\|[^0-9])\zs[0-9]{10}\ze([^0-9]\|$)/\=strftime("%c",submatch(0))/g<CR>