Update styles

* Use the shorthand `font` property when possible.
* Be more explicit with the `background` and `list-style` properties.

Close h5bp/html5boilerplate.com#115.
Remove `main.css`

File is not longer needed.
Base64 encode the background images.

-2 HTTP requests and CSS size is +1.5KB of what it was before grunt-uncss (8.47KB minified without gzip).
Remove old IE hacks.
Update normalize.css to v3.0.1.