Notable changes:
- Over 150 commits from 22 contributors!
- License change to the 3-Clause BSD License
- Python 3.x support
- Refactoring of SelectConnection ioloop
- This major release contains certain non-backward-compatible API changes as well as significant performance improvements in the BlockingConnection adapter.
- Non-backward-compatible changes in Channel.add_on_return_callback callback's signature.
- The AsynchoreConnection adapter was retired