[build2] Python Wrapper with Pybind11, Calling Python, and Renaming Libraries

[Markus Pawellek]

Thank you very much.
I was able to successfully integrate your ideas.
The files look much cleaner now.

Is there a way to further extend the
install and uninstall commands of build2?
Currently, one has to make sure to call 'python -m pip install .'
inside the directory of the build configuration.
I am still doing this with the Makefile.
If it would be possible to extend the installation process then
by calling 'b install', build2 would be able to call
the given command inside the build directory of any chosen configuration
without intervention of any external tool.

Greetings
Markus