Issue #143. Change formatting from html to markdown

This changes all fields that previously used HTML to now use Markdown.
This fixes a bunch of issues:

1. no one likes writing raw HTML---Markdown is a lot easier
2. conferences don't put their content in HTML, so I usually have to
   go back and fix everything---Markdown is an easier format to
   work with and convert everything to
3. HTML is harder to make safe from XSS and similar issues
4. HTML is easier to make HTML mistakes in causing bad rendering
   for pages with problems

Given all that, I knew I wanted to switch to either reST or Markdown
and it was just a question of when. That when is now.