Flake8 formatting cleanup

[tburrows13]

Nothing of any substance is supposed to have changed in this PR. I've simply gone through all the flake8 warnings and corrected the code where necessary, or specifically ignored that type of error where it conflicts with black.

Most notable changes:
All raw except: have been replaced with except Exception:
All assigned lambdas have been replaced with a def
The Travis build will now fail when flake8 detects undefined variable names. (Removal of --exit-zero on the important check)
All regex strings with backslashes have been made 'raw' by putting an r at the start of the string. This prevents a DeprecationWarning.

[coveralls]

Coverage decreased (-0.2%) to 64.786% when pulling 58c4c03 on tburrows13:fix-warnings into 24ebfdb on Zulko:master.

[tburrows13]

I'm ready for this to be merged as well.