-------------------
- Add ``TChannel.is_listening()`` to determine if ``listen`` has been called.
- Calling ``TChannel.listen()`` more than once raises a ``tchannel.errors.AlreadyListeningError``.
- ``TChannel.advertise()`` will now automatically start listening for connections
if ``listen()`` has not already been called.
- Use ``threadloop==0.4``.
- Removed ``print_arg``.