Added Ben Henning's GSoC2013 work: premake build system.

premake/README-windows.txt

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+Use the Visual Studio batch files (located in the VisualC folder) to
+conveniently generate solutions for Visual Studio 2008, 2010, and 2012.
+It also contains a cleaner script and a convenient script for automatically
+running all the test suites.
+
+There is a script (check.bin.compatibility.vs2010.bat) in VisualC\build-scripts
+which will build <sdl_root>\VisualC (which is not generated by this premake
+system) and build SDL2.dll using the generated SDL2.sln in the VS2010 folder. It
+will copy the SDL2.dll over to each test project in <sdl_root>\VisualC and
+subsequently run those tests to verify binary compatibility between the SDL2.dll
+that came from the premake solution and the executables which were built using
+the old solution files.
+
+The windows project currently depends on most of the libraries inherently
+added to the links list by Visual Studio. The additional libraries SDL2 depends
+on are as follows:
+
+  -imm32
+  -oleaut32
+  -winmm
+  -version
+  -OpenGL32
+  -DirectX
+
+OpenGL32 is an optional dependency. If it is not located for whatever reason,
+SDL2 will build fine without it. DirectX is another optional dependency for
+SDL2. Unlike the manually-created VS projects, the meta-build system supports
+not having DirectX support and still being able to build and run through most of
+the projects (using the OpenGL renderer or the software renderer).
+
+Run the clean script to clear out the directory of VS-related files and
+binaries.
+
+Ben:
+Please note that the script for building the VS2012 solution from the
+command prompt seems to not be working properly. This issue is
+currently unresolved.