register the different ezpt transports as separate transports in their own right
add a way for the user to configure ezpt transports via a file, and document this
Don't pass the transport_name to the base transport.

We don't need to do so yet.
add some more documentation
Re-applying George's previous intentions
- Rename ezpt transports to 'ezpt_<transport>'.
- Change the environment variable name.
Include the ezpt transports in our integration tests.
add tests to setup.py