Add XNET error/exception info in docstrings

[jashnani]

We should update all public docstrings to include a 'Raises' section (where applicable) to describe what errors/exceptions can be thrown from that class, function, property, etc.

ex: http://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html

The motivation for this came from wait_for_transmit_complete. The user might use a timeout with this function and intentionally want an error to be thrown. They will likely want to handle the error and should have enough info on how to do it.