Made ironfroggy's suggested change of passing JulesEngine around.
Added new plugin type, reorganizing things around JulesEngine.

The next change to land should be me fixing up rendering to work in
some particularly nice manner that I have yet to determine. It needs
to work in multiple phases, which is unsettling.
Some more structural changes to allow for posts to work how I'd like.

Posts should be able to interlink using canonical URLs next commit,
maybe, I hope. :)
Canonical URLs/links work! Woooooo!