Support rendering a subset of CommonMark in the chat

[robinlinden]

The types implemented in this PR are bold, italic, and monospace text.

Resolves #238

[roihershberg]

What about Markwon?

It has even a live rendered editor which can be binded to the message edittext.

[robinlinden]

Back when prototyping this (this PR is not complete at all, just for a few testers to check it out and see what they though), I looked at different implementations but didn't find one I was 100% happy with, and since I only want a tiny subset of markdown, I figured the easiest thing would be to hack together a small parser (i.e. the regex is not intended to stay).

The things I want:

• The formatting characters should not be removed when applying the style.
  • i.e. `text` should be rendered as `text`. This can be optional, but by default I want it to display all characters received.
• Only emphasis, strong emphasis, strike-through, inline code, and code blocks.
  • It shouldn't be possible to try to inline images in messages, hide links, or apply colors etc.

This is apparently half a year old now, so if there are any small-ish markdown-implementations that check my boxes, that would be nice. :P I did look at Markwon, but I don't recall why I didn't like it, so maybe it's a fine option.

[roihershberg]

From what I understood you can control pretty much everything in Markwon.

Why not remove those characters? Maybe it's possible to remove them like the default behavior but copying them when copying the message.