Revert "Remove unnecessary PEP references"

This reverts commit fa96c4f5d54d0628a492413d44edcd37923f62c2.

Removing these references causes the docstrings to not pass
the PEP-257 check when pep257.py is run on itself.

Fixes #25

Change-Id: I70471d2b120d93895fad61fca8bd8627d9012f19