Some of Motor's code examples are automatically copied from PyMongo but aren't correct for Motor. sphinx-build now warns about these (I put some logic into motor_extensions.py to catch them).

Additionally, many of Motor's code examples use "gen.coroutine" and "yield", which are Tornado-specific. Better to use "async" and "await" in docstrings, since that's a modern style and is identical in Tornado and asyncio.

The Tornado tutorial will still demonstrate Python 2-style code with "gen.coroutine" and "yield".