Reduce fractions before outputting class names to avoid redundant CSS

A lot of redundant CSS was getting created. For example, -width-1-1, -width-2-2, etc all create width:100% rule. Similar with all the fractions that result in 25%, 50%, etc. Implemented this algorithm reduce fractions before output. 

https://gist.github.com/chrisross/5935988

You can see the amount of code removed in the fraction-grid.css diff.