Displayed dates in the blog templates are now all taken from meta['date'],
which can be set by the 'date' metatag in the blog post but defaults to the
date obtained from the post's slug (i.e. what subfolder the post is in).

- Added support for metadata in blog entries
- Modified blog/index.html and blog/entry.html templates to use metadata
- Migrated the most recent post over to just a .rst file and added metadata

This increases the speed of the site by not requiring the site and blog code to
be imported on every request - just those that are relevant. It also splits the
code into modules which are easier to work with.