Helper methods for swift users

Swift brings stronger type-checking to Xcode, but ObjC-bridged frameworks are full of AnyObject's and Any's. The idea is to add overloaded methods that take type-checked arguments to help catch bugs early. Class extensions make it opt-in.

Adds a small processing time to "encode" attributes into a dictionary to pass along.

Ideally, the base ObjC implementation could use "modern" ENUMs instead of string keys, which would be bridged cost-free to swift.