Parse talk body from github

[wgao19]

This may require some kind of protocal on our talk proposal's content. We can try to enforce this by editing the issue template. Then, we need to parse the talk body to display the portion we hope to display on the website.

• related loc

[wgao19]

we now have some crude parsing from #52, it also relies on certain format of our talk proposal, namely, the description to show up on home page should go between the lines:

<!-- intro starts -->

description should go here

<!-- intro ends -->

but what goes inside descriptions still needs a bit parsing (i.e., picking up links, etc.)

what has been implemented didn't take much time, although, if this thing goes significantly more complex, we should probably think more thoroughly how we want this properly done.