glib-genmarshal is now a Python script instead of a compiled program, so
we need to:
-Remove the projects that are used to build the glib-genmarshal sources.
-Generate the full glib-genmarshal Python script from glib-genmarshal.in
-Make Python a hard build-time requirement, since we use this tool
in many parts of the stack (and it is the case for glib-mkenums).
-Tell people in the Visual Studio build README.txt files that Python
2.7.x or 3.x is now required for the build/"install".
It was suggested that the project files be moved here as we don't actually
need to go two directory layers from $(srcroot), and would help us to
standardize on things in the future across the board.
