gravatar: fix generated HTML to validate correctly

This introduces a simple alt="" value which is required by the new
HTML5 validation, and also fixes the URL to use the correct &amp;
syntax.
feeds: don't append the subtitle to the page title.

Since the subtitle is already passed to the feed itself, repeating it
here can only cause redundancies. Furthermore with the current version
of Typo, it's possible to change the format of the pages' titles.
akismet: replace vendored, hacked, old akismet version with 1.0.0

The new version can be loaded through Gemfile instead and might work a
little better.
Merge pull request #143 from Flameeyes/master

Small fixes