Support Markdown emoji

[Sebclem]

Is your feature request related to a problem? Please describe.
I'm using a lot of markdown emoji in my commits message, but in gitui, the emoji are not parsed.

Describe the solution you'd like
Replace all markdown emoji by it's Unicode equivalent.

I have found this lib that can help: https://lib.rs/crates/gh-emoji

Describe alternatives you've considered

Additional context

This should look like this:

[extrawurst]

Hi @Sebclem I dont find that feature particularly important but I wouldn't mind it if anyone wants to pick it up👍

Note: In case anyone wants to tackle this - make sure to not run the parser on every draw but just on the cache of commits we keep in memory

[andrewpollack]

This looks like a fun issue 😄 mind if I give this a go?