Refactor HTML into a more semantic structure and rework styles to be much less specific

@jeffkamo @tedtate @scalvert @rrjamie 
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#### Things I did:

1. I've changed the class naming structure to something more sane. Approaches a BEM style. Should make overriding styles in the future much simpler.
1. Switched to using autoprefixer to make our styles easier to manage. Builds in the same way.
1. Rewrote the way centering works to be a lot simpler. 
1. Removed the gridded fluid settings as they were never documented and rarely worked properly.

#### Tested working on:
* Chrome Latest,
* Firefox Latest,
* iOS 4.2.1+,
* Android 2.3+

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 Thinking this needs a minor version bump because it's so different.