Users can now configure Review Bot to run pydocstyle, a tool for checking 

compliance with Python docstring conventions. 
Pydocstyle is not added to the install requires list and users will 

need to manually install it to use it.
Pydocstyle defaults to using the PEP 257 docstring convention but users

can add a list of errors to ignore which will override the convention.

Tested dependency check by running reviewbot worker command without 

pydocstyle installed
Tested pydocstyle by adding new configuration to Review Bot integration 

and publishing a review. Also tested with errors added to ignore list.