add STREAM_BW event handler

Adds STREAM_BW event handler class and tests.

This patch series includes an aliasing of is_valid_circuit_id to is_valid_stream_id. I am not sure how to provide context to the associated pydoc to keep it linked to the alias assignment.

These patches may not want to apply cleanly due to my end-of-file configuration instructions to my text editor. But, the changes are whitespace clean and do not add anything but working code. Hopefully, I will not continue working near the end of files and this will not crop up again.

Trac:
Username: robinson