First was for mypy compatibility, but is no longer needed.
Second is removed by going inheriting (Iterable[bytes],
Container[bytes], Sized, Reversible[bytes]) instead of
Sequence[bytes]. Should presumably catch more errors when using __getattr__
* py3 done
* have to have specific version, to much changes
* py2 done
* merge py2 and py3 version
* fix duplicate definition in mypy
* apply version specific def
* rename ContextManager, single line for import
