Support Flake8 plugins

[radekjg]

Two flake8 plugins add new types of violations:
flake8-import-order adds I
flake8-blind-except adds B
flake8-pep257 adds D
flake8-snippets adds S
flake8-double-quotes adds Q

[Bachmann1234]

Thanks for the PR ill try and look at this in detail soon!

[Bachmann1234]

@dreamwalker Looks good to me. Add yourself to the AUTHORS file and I release this.

[coveralls]

Coverage remained the same at 99.23% when pulling 0eb57db on dreamwalker:fixes/support_flake8_plugins into 83ee60d on Bachmann1234:master.

[coveralls]

Coverage remained the same at 99.23% when pulling b0e5bb2 on dreamwalker:fixes/support_flake8_plugins into 83ee60d on Bachmann1234:master.

[coveralls]

Coverage remained the same at 99.23% when pulling 30246b8 on dreamwalker:fixes/support_flake8_plugins into 83ee60d on Bachmann1234:master.

[Bachmann1234]

fantastic. ill merge and release sometime soon. Hopefully tonight unless life gets in the way.

Thanks!