Add additional functions to pyxx.arrays

[nathan-hess]

Major Changes and Improvements

• Added new functions to pyxx.arrays module, and added tests and documentation for all new code
  • pyxx.arrays.check_len_equal() and pyxx.arrays.is_len_equal() compare lengths of input arrays or other objects
  • pyxx.arrays.is_array_equal() checks whether multiple arrays have the same size and content (within a given tolerance for numeric content)
• Added new context manager to Python test code that can capture text printed by running code (useful for testing that desired content is printed)

Bug Fixes

• Changed format of package version number in pyxx/__init__.py to use string instead of f-string
  • See reference links below. It appears that setuptools requires specific syntax for reading attributes from a file, and the previous f-string did not function as expected. One possibility (although it would require more debugging to determine) is that setuptools was attempting to read the f-string statically and obtaining unexpected results.

Minor Updates

• Reorganized documentation files
• Added missing test for pyxx.files.File class

Notes and References

• Type checking
  • Unsupported operand types for + (List[A] and List[B]) when B extends A python/mypy#3933
• Reading package version when building package
  • https://stackoverflow.com/questions/58202909/modulenotfounderror-when-using-setup-cfg-and-version-accessed-with-attr
  • Support attr directive with static evaluation pypa/setuptools#1753
  • Read Version Number from the Package in setup.cfg pypa/setuptools#2530
  • python setup.py develop fails with version = attr: pkg.__version__ in setup.cfg pypa/setuptools#1724