First attempt at twisted sasl transport
Basic working sasl transport support
Handle schema setup in sasl demo
Rough start on sasl transport pooling
Process challenges in a separate thread

These may result in blocking network calls, so we need to use
deferToThread to avoid blocking the reactor.
Working pooling with sasl transport
Rename sasl_host, sasl_service params to host, service
Add sasl_cred_factory docs to pool docstring
Read outer and inner frame lengths separately
Subclass to remove duplicated code, handle incomplete frames
Call correct parent class for dataRecvd, dispatch
Add other system keyspaces to list to ignore
Merge remote-tracking branch 'driftx/master' into sasl-support

Conflicts:
	telephus/pool.py
	telephus/protocol.py