This updates translate-tag.rb to parse all strings. This means that
we can add items such as {{ site.name }} into the source strings
and the plugin will do the rest. We no longer need hacky a
hacky workaround.
Adds in support for https://github.com/signalapp/jekyll-simple-i18n.
The plugin did not work with the github-pages gem, so github-pages was
switched with jekyll (which is what the current i18n branch does anyway).
