build: Add a set of NMake Makefiles

build: Add a set of NMake Makefiles

This adds a set of NMake Makefiles that is able to:

* Compile Vala from the generated C sources in a release tarball
* Compile Vala with an existing Vala build/installation from the
  original Vala sources.

What is not done currently:
* Generating sources in gobject-introspection/ using Bison/Flex.
* Re-generating the *.vapi files in vapi/ using existing .gir
  files.
* Running the tests
* Building vapidocs
* Preparing for the build directly from a GIT checkout.

This is done in a modular fashion so that one may specify the
INCLUDEDIR and LIBDIR if the include and library paths for GLib
are not in the compiler's default paths.

This NMake Makefile set supports Visual Studio 2008 and later-
please note that I did not (and am not intending to) update the
.vala/*.c/*.h files to make the support work.