Port from yeoman to lineman

Yeoman was the easiest thing to get started with, but I've never really been a fan of it. It's just too bloated. This ports the app over to using lineman. As part of that, I also switched the CSS from sass+compass to stylus+nib.

/cc @searls

## TODO

* [ ] get octicons working
* [ ] script/bootstrap
* [ ] script/server
* [ ] enforce SSL
* [ ] [Deploy to heroku](https://github.com/testdouble/lineman#heroku)