Inspired by tulip, have every module define a __all__ list and import *
from the top-level module.
Rename transport.set_defaults() since we don't want this to be a
top-level set_defaults() function as there may be multiple.
Also, rather than configuring flake8 to allow star imports, just exclude
the __init__.py files from flake8 checks.
03aafcb49c