* flake8 updates and cleanups
* Update to flake8 3.7.9.
* Update to flake8-bugbear 20.1.4.
* Only ignore errors in stub files.
* Remove obsolete error counts.
* Sort error codes alphabetically.
* Don't ignore the following errors (unneeded):
* E704 Multiple statements on one line (def)
* W504 Line break occurred after a binary operator
* B303 __metaclass__ used
* Remove obsolete comment
* Ignore F822 undefined name in __all__
All Python 3 versions supported by typeshed (3.4+) have enum as part
of the standard library.
Make the third-party Python 2 version consistent with the Python 3 version.
pathlib2 is the Python 2.7 backport of the pathlib module from Python 3.
Hence we use the same stub file for both.
The maintainer of pathlib2 granted permission for stubs to be added in
mcmtroffaes/pathlib2#44.
Make the Python 2 and 3 concurrent.futures stubs identical so fixes get
applied to both.
For example, #1305 and #2233 fixed the same problem at different times,
as did #1078 and #1911.
By making the stubs identical, we apply the fix from #1711 to Python 2.
Fixes#2234.
The dict stub was referring to an instance, not the type, leading to
__call__ being considered when using as a decorator, rather than
__init__.
mock is a backport of the stdlib module and should be defined the same.
