Update Python wrapper documentation
The wrapper documentation is several years out-of-date and contains inaccuracies.
Wrapping/Python/README.md
This file currently contains general (but outdated) information on the Python wrappers, and it should be brought up-to-date and moved to Documentation/Doxygen. The readme for Wrapping/Python should instead contain information about the contents of that directory (vtkPythonAppInit and vtkmodules).
Wrapping/PythonCore/
This directory currently has no documentation, but should have some. This directory contains extension classes and utility classes that are used by the Python wrappers.
Wrapping/Tools/README.txt
This file currently contains instructions on how to run lex and yacc to build the parser. It should be expanded to give a high-level overview of how the wrappers are constructed. And it should be re-named to README.md.