greenio, tpool: python3 compatibility

Also:
- PEP-8
- check both EAGAIN/EWOULDBLOCK
- use system implementation of GreenPipe.readinto()
Python 3 compatibility fixes

Closes GH-102
Closes GH-103
Closes GH-104
wsgi: websocket: Reformat code + tests (PEP-8)
Travis: Enable fast build finish
tests: Update bundled mock library to 1.0.1
PEP-8 fixes; six.next for Python3 compatibility