Define .putMslEncodable(MslEncodable, MslEncoderFactory, MslEncoderFormat)

[wmiaw]

At the moment, MslObject and MslArray accept MslEncodable instances but hold onto them as objects of their original concrete type. However this can create a problem because when someone tries to parse a MslObject or MslArray, they are expecting a MslEncodable to be parsed out and returned as a MslObject, not as an instance of the original concrete type.

The current code pushes this problem out to the caller which is why certain MslEncodable classes encode or encode+decode their MslObject or encoded byte[] representations before returning them. There are corresponding FIXME comments. The right solution, although it comes with higher computational overhead, is probably to add a .putMslEncodable() function that must be used for MslEncodables, and reject MslEncodable values from the .put() function.