Site Comment Updates

I've made a few updates to how my web blog handles user comments:

• Anonymous users on the Internet are now able to edit or delete their own comments for 2 hours after posting them (this is cookie-based).
• All e-mails sent from this site are now formatted in HTML and will render Markdown text, so if you subscribe to a comment thread you can see the future comments rendered out as HTML in your email client.
• I added a "Quick Delete" function for me, so that when a spam bot posts spam I can click one link in my e-mail that instantly deletes the comment without me needing to log in or do anything.

The gory technical details are in the pull request.