WIP: Support python CMakeLists.

TL;DR

Support running python scripts as CMakeLists:

Description - Desired behavior

When there is a CMakeLists.py file in the directory, cmake would run it instead of looking for CMakeLists.txt. Where CMakeLists.py is a minimal python file (e.g. without any non-builtin modules other than cmake).

There would be a minimal cmake API for python (1-3 functions) with a few python modules for the actual implementation. For example, cmPythonAPI_runCommand would run a command. then, the python module would implement cmake's commands (e.g. add_library, etc).

Task list

• Support cmMakeFile abstraction: cmMakeFile should be able to read both .txt files and .py files according to the files in the current directory (.py should be preferred).
• In order to support this command in python, move cmake_minimum_required validation code from Configure to its own command.
• Implement the CMake->Python API: should not be more than 2-3 function (currently unstable):
  • cmake_run_command(name, *args, **kwargs): should parse a list of parameters and run the command "name".
  • cmake_get_var(name): get a cmake variable.
  • cmake_put_var(name, object_value): set a cmake variable.
• Implement rich cmake Python API from the functions above.
• Implement mPyMakefileProcessor::Configure to run the CMakeLists.py file.

Please let me know about any issues, problems, or suggestions. Thank you.