Adds support for MessageBus.transport_codec which can be used to optimise
performance of transport

- Oj can be used as a serializer vs JSON which is a bit slower
- Users can implement custom codecs
- OjFast can be used as a serializer for efficient user_id lookups

Backwards compatible change, switching codecs to OjFast will invalidate all
existing storage.

Work in progress

Sadly spec suite is not quite passing cause encoded data explodes if
\x00 is in the stream, need to figure out why

Bench though is spectacularly good, so we are making progress

- Allow redis backend to handle \u0000 in exceptional cases like
the unsupported Marshal codec

- Ship only Oj and JSON codecs out of the box

- Add more benchmarks to show when packing user ids helps vs hinders

- Update readme

Co-authored-by: Rafael Garcia <rafbgarcia@gmail.com>

Co-authored-by: Rafael Garcia <rafbgarcia@gmail.com>