3.1.0 Sass Version

sass conversion.

sass files are:
```
build/assets/font-awesome/sass
    config.rb
    sass
```

I've used compass to simplify the font face import.

I've structured `build/assets/font-awesome/sass/_icons.sass` so that each icon is also a mixin.

There is also a generic `icon` mixin.

I've merely removed `{;}\s$` from font-awesome-ie7. ie7 is of no relevance to the reality of my clients or myself.