Using CoreParse to parse NSS file

Fixes #33.

This pull request integrates CoreParse to parse the NSS file. CoreParse uses BNF syntax and thus makes extending the NSS format fairly easy. The next step is to provide @media queries per #3, which is my real goal here.

I just submitted a pull request to CoreParse that adds a podspec file. Once that gets approved I will place the podspec file in the CocoaPods Specs repo and I will update the Podfile in the NUI Demo accordingly.