New``__f2py_numpy_version__`` attribute for f2py generated modules.
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Because f2py is released together with NumPy, ``__f2py_numpy_version__``
provides a way to track the version f2py used to generate the module.

Add gh-16594 to NumPy 1.20.0 release notes.
DOC: Add gh-16594 to NumPy 1.20.0 release notes.
