Corrected NSURL transformation
added description for toDictionary
added versions of toDictionary & toJSONString which support exporting specific properties
Merge branch 'master' of https://github.com/icanzilb/JSONModel
Merge pull request #122 from BillinghamJ/partial-serialization

Options for partial serialization
Merge pull request #119 from BillinghamJ/nsurl-transformer

Corrected NSURL transformation