Scheme parser

As promised, I'm submitted a PR for a basic scheme parser for a r5rs-like scheme.  It does not support the full numerical tower.

It could probably stand some code review before the merge.  

Additionally, it has 77 tests, but 1 failure.  The pesky quotation mark test (see below)  So advice on fixing this would be greatly appreciated. 

![screenshot from 2014-01-04 09 40 46](https://f.cloud.github.com/assets/148626/1843643/29e25ac0-74d9-11e3-8a3b-ff4612bcda97.png)