Deprecation warning for `\*\*` in docstrings

[ashwin153]

For example,

https://github.com/PagerDuty/pdpyras/blob/19971ec2df9ab854a91b95a25de452483ea57af0/pdpyras.py#L481

Causes the following deprecation warning.

DeprecationWarning: invalid escape sequence \*

Here's a reproduction.

import warnings
warnings.simplefilter("always")
x = "\*\*kwargs"
# <stdin>:1: DeprecationWarning: invalid escape sequence \*

Definitely not a pressing issue, but it pollutes my build logs. I'd suggest adding another slash (e.g., \\*). Sphinx appears to render \\* and \* the same way. For example, here's how they both render on a sample site.