Improve test speed

Rather than instantiating a new Regularity instance for each spec, I've added a reset method that blanks the string and added before and after blocks to the specs that instantiate a Regularity object on the first spec and reset it's string after each spec. 

![screen shot 2013-10-03 at 13 01 24](https://f.cloud.github.com/assets/35007/1261108/658a91d0-2c24-11e3-86d1-143ddf17b56a.png)

Like this library and would love to contribute!