Module rename: mod_pywebsocket -> pywebsocket3

[Adam Rice]

We are renaming the "mod_pywebsocket" module to "pywebsocket3" in order to enable submission to PyPI.

https://github.com/GoogleChromeLabs/pywebsocket3/pull/33

This will mean that all *_wsh.py handlers which explicitly mention mod_pywebsocket will need to be updated, but it should be a simple search-and-replace operation.

As there are no new features, there is no urgency to update, unless you want to switch to the PyPI package.

Thanks to Henrik Skupin for doing the actual work on this.