Mark slow tests, update `__eq__` methods, pin reqs

[brl0]

Summary of changes:

• Add --skip-slow option (slow tests are still run by default)
• Mark various tests as slow based on run time as captured by pytest --durations=0
• Pin numpy<1.20 on MacOS due to test failures
• Add feature to Geometry class __eq__ method that if other object is a container, the equality method on the container is called, so now performing an equality check between a geometry object and a geometry array should return correct results, which should be a bool array, whereas previously it would simply return False because the objects were not the same immediate type.
• Add feature to GeometryArray class __eq__ method to allow comparison of an individual element to all objects in the array, returning an array of bool.
• Add NotImplementedError for __contains__ method.
• Sort imports on modified files
• Add some type hints to parquet functions

Let me know if there are any questions or concerns about any of these changes.

[brl0]

In addition to the changes above, Dask has now been pinned on Mac due to incompatibilities with pyarrow>=2.
Also, I updated the change log for the next release.

@jbednar, thanks for your time reviewing and your input. Let me know if you have any additional questions or concerns.

I think this should be ready to merge.