Gruntfile.js: Make usemin pick up cssmin's options
Clean up `.gitignore`
Base64 encode the background images.

-2 HTTP requests.

Before: 15.9 kB → 5.3 kB → 1.23 kB (gzip)
After:  20.1 kB → 10.65 kB → 3.39 kB (gzip)
Remove old IE hacks.
Update normalize.css to v3.0.1.