Add markdown rendering

[philipbutler]

Resolves: #38
Allows simple markdown rendering. I am observing though that *s aren't rendering as bullets.

Before:

After:

[b9r5]

Hey Phil - the visual diff looks really could. Could you check a couple of things:

1. That links render as links - try both https://www.example.com and [example](https://www.example.com).
2. That markdown rendering does not interfere with mathjax or vice versa - try some sample LaTeX like $$E=mc^2$$ along with some markdown.

Also please add a test to test_leaderboard.py that puts some markdown in the description, then scrapes the html with beautifulsoup and verifies that it contains the markdown rendered into HTML? (I hope that makes sense.) Test 1 above should be automated as pat of this.

I don't know of a way to automate test 2, so I guess it has to be manual for now, unless you can think of think of some way to automate it (but I wouldn't spend too much time on it if it's difficult - for example, screen scraping wouldn't be worth the effort.)

I still need to check over the diff to look at the content security policy.

Thanks!

[philipbutler]

@b9r5 Yes that all makes sense! On it