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Move Interface hashing and comparison to C; 2.5 to 15x speedup in micro benchmarks

Included benchmark numbers:

Current master, Python 3.8:

.....................
contains (empty dict): Mean +- std dev: 198 ns +- 5 ns
.....................
contains (populated dict): Mean +- std dev: 197 ns +- 6 ns
.....................
contains (populated list): Mean +- std dev: 53.1 us +- 1.2 us

This code:

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contains (empty dict): Mean +- std dev: 77.9 ns +- 2.3 ns
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contains (populated dict): Mean +- std dev: 78.4 ns +- 3.1 ns
.....................
contains (populated list): Mean +- std dev: 3.69 us +- 0.08 us

So anywhere from 2.5 to 15x faster. Not sure how that will translate to
larger benchmarks, but I'm hopeful.

It turns out that messing with ``__module__`` is nasty, tricky
business, especially when you do it from C. Everytime you define a new
subclass, the descriptors that you set get overridden by the type
machinery (PyType_Ready). I'm using a data descriptor and a meta class
right now to avoid that but I'm not super happy with that and would
like to find a better way. (At least, maybe the data part of the
descriptor isn't necessary?) It may be needed to move more code into
C, I don't want a slowdown accessing ``__module__`` either; copying
around the standard PyGetSet or PyMember descriptors isn't enough
because they don't work on the class object (so
``classImplements(InterfaceClass, IInterface)`` fails).

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