Added support for GME (Game_Music_Emu).

This makes it possible for LÖVE to play music files for NES, SNES, MegaDrive,
and many more. It's pretty cool.

The feature is disabled until each platform is ready to link with GME. Packages
exist for Debian and Arch, and it compiled without any issues in MSVC++, so
I don't expect this to a problem for anyone.

src/modules/sound/lullaby/Sound.cpp

@@ -18,11 +18,14 @@
  * 3. This notice may not be removed or altered from any source distribution.
  **/
 
+#include "common/config.h"
+
 #include "Sound.h"
 
 #include "ModPlugDecoder.h"
 #include "Mpg123Decoder.h"
 #include "VorbisDecoder.h"
+#include "GmeDecoder.h"
 //#include "FLACDecoder.h"
 
 namespace love
@@ -64,6 +67,10 @@ sound::Decoder *Sound::newDecoder(love::filesystem::File *file, int bufferSize)
 #endif // LOVE_NOMPG123
 	else if (VorbisDecoder::accepts(ext))
 		decoder = new VorbisDecoder(data, ext, bufferSize);
+#ifdef LOVE_SUPPORT_GME
+	else if (GmeDecoder::accepts(ext))
+		decoder = new GmeDecoder(data, ext, bufferSize);
+#endif // LOVE_SUPPORT_GME
 	/*else if (FLACDecoder::accepts(ext))
 		decoder = new FLACDecoder(data, ext, bufferSize);*/