emoji size when using native fonts option

[agnauck]

When using the native font option on Windows the unicode characters are not monospaced and vary in width. Emojis are not displayed nicely in columns then.

I am suggesting to add with and height to the css like the following:

span.emoji-mart-emoji {
  width: 36px;
  height: 36px;
}

See also:

[agnauck]

The problem is solved after I switched to NotoColorEmoji font.
Compared to the Microsoffts Segoe UI Emoji font NotoColorEmoji has fixed width.

Maybe its worth mentioning differences with OS fonts somewhere in the docs.

see also #71