Tagnostic

I think this subclass of HTMLParser will help us simultaneously render
scored content and Markdown styling without getting confused. Details
to come.
Markdown support

Votes are displaying misaligned three characters to the right per
paragraph after the first, but when posts were plaintext, there were
no such things as paragraphs, so I think this is still an improvement.
vote indices refer to inferred plaintext; slimmer ballot box

This fixes the misalignment we were seeing in the parent commit.
render tags with attributes (notably, hyperlinks) properly
merge branch 'markdown'

Conflicts:
    core/views.py