Updated to use a header template.

Updated to use a header template which accepts a `currentpage` variable to set the active class for the navigation -- you'll have to do the same for the other pages. Added a footer template as well because that seemed like something cool to do. Also changed to `default` layout so that the assets are relative to root so you won't have to use the `default_subdir` anymore.

Also, you don't have to commit the _site directory, GitHub will compile that automatically.

:shipit: