Remove superfluous buffering

Here with Leif's suggestion... I remove BananaPhoneBuffer...
and completely remove a superfluous layer of buffering.
We use the handshake method to start and direct the
encode/decode coroutines into the appropriate circuit stream.
Merge branch 'david-bananaphone' into david-bananaphone-public-options

manually resolved Conflicts:
	obfsproxy/transports/bananaphone_transport.py