Serialization to/from JSON should be streamable

This may be useful for large numbers of large messages on post/get. Need to do some testing to see if it's worth doing. Can we do this in a performant way, while minimizing memory usage?

Consider WSME to see if it can do this, and is fast enough for our needs. Otherwise, we may need to roll our own. Shouldn't be very difficult, and could be template-based or something (TBD).

See also: http://thechangelog.com/ijson-parse-streams-of-json-in-python/