Keep imports alphabetically sorted and their order homogeneous across
Python source files.
The isort project has more feature and is more active than the
flake8-import-order plugin.
Most issues caught were simply import ordering from the same module.
Where imports were purposefully placed out of order, tag with
isort:skip.
A common use case for this is a class like `namedtuple`, which has a public `_replace` method that is so-named in order not to conflict with arbitrary user-provided attributes.
Rejected spellings include:
* `:meta not-private:`
* `:meta private: False`
