for review: updates templates, minor dotfile cleanup, grunt config

For the most part, this PR focuses on DRYing up the templates, but there is also some cleanup in a couple of places, like .gitignore. (fwiw I'm a maintainer for Assemble, I saw a few places where we could make things easier and just wanted to lend a hand)

There are a few other things we can do in the templates to make them easier to maintain. For example, I think we can get rid of most of the `{{#markdown}}` tags in the includes and pages since we're already passing the content through the markdown helper in the layout. 

Also, If you'd like to see this broken into several PR's just let me know.