Some minor clarifications in the documentation of pathlib + inheritance diagram
Remove the tuple reuse optimization in _Pickle_FastCall.

I have noticed a race-condition occurring on one of the buildbots because of
this optimization. The function called may release the GIL which means
multiple threads may end up accessing the shared tuple. I could fix it up by
storing the tuple to the Pickler and Unipickler object again, but honestly it
really not worth the trouble.

I ran many benchmarks and the only time the optimization helps is when using a
fin-memory file, like io.BytesIO on which reads are super cheap, combined with
pickle protocol less than 4. Even in this contrived case, the speedup is a
about 5%. For everything else, this optimization does not provide any
noticable improvements.
Remove explicit empty tuple reuse in cpickle.

PyTuple_New(0) always returns the same empty tuple from its free list anyway,
so we are not saving much here. Plus, the code where this was used is on
uncommon run paths.
Use PyDict_GetItemWithError instead of PyDict_GetItem in cpickle.
Modify testAssertDictEqualTruncates so implementation isn't dictated.
Modify testAssertMultiLineEqualTruncates so implementation isn't dictated.
Move assertFalse out to separate class.
Move assertTrue out to separate class.
Split out separate Asset super-class.
Invert sense of self.test.
Move _baseAssertEqual out to separate class.
Make msg a required keyword argument, reducing duplication.
Move assertNotEqual out to separate class.
Move assertAlmostEqual using places out to separate class.
Move assertAlmostEqual using delta out to separate class.
Move remaining assertAlmostEqual logic to separate class.
Move assertNotAlmostEqual using places out to separate class.
Consolidate test logic to be within specific AssertAlmostEqual classes.

Specifically, remove the shortcut from the AssertAlmostEqual class and
push it in to the AssertAlmostEqual{Places,Delta} test methods.
Define AssertNotAlmostEqualPlaces as the inverse of AssertAlmostEqualPlaces.
Move assertNotAlmostEqual using delta out to separate class.