base64.decodestring is depricated in Python 3.1 and is removed in 3.9

[frydaho]

After installing I received this error from line 93 in feedparser.py:

_base64decode = getattr(base64, 'decodebytes', base64.decodestring) AttributeError: module 'base64' has no attribute 'decodestring'

I can't seem to create a new pull request, or I would just push my changes... Very easy fix: just change the end of line 94 to read base64.decodebytes and everything runs like a dream.

Thanks for writing this! It's very awesome. :)