Alexander + RawRepresentable = ❤️

[cocoahero]

This PR adds some new functionality:

• Adds generic decode<T>(transform: JSON -> T) -T? function.
  • This allows users to decode something that might not be JSONDecodable.
• Adds decode<T: JSONDecodable>(type: T.Type) -> T? function.
  • This builds on the previous function addition to help clean up code paths such as let author = JSON["author"]?.decode(Author).
• Adds decode<T: RawRepresentable>(type: T.Type) -> T?
  • Allows a user to decode JSON into a single enum instance.
• Adds decodeArray<T: RawRepresentable>(type: T.Type) -> [T]?
  • Works like its JSONDecodable sibling, allows you to decode an array of enums.