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/GmeDecoder.h

@@ -0,0 +1,68 @@
+/**
+ * Copyright (c) 2006-2012 LOVE Development Team
+ *
+ * This software is provided 'as-is', without any express or implied
+ * warranty.  In no event will the authors be held liable for any damages
+ * arising from the use of this software.
+ *
+ * Permission is granted to anyone to use this software for any purpose,
+ * including commercial applications, and to alter it and redistribute it
+ * freely, subject to the following restrictions:
+ *
+ * 1. The origin of this software must not be misrepresented; you must not
+ *    claim that you wrote the original software. If you use this software
+ *    in a product, an acknowledgment in the product documentation would be
+ *    appreciated but is not required.
+ * 2. Altered source versions must be plainly marked as such, and must not be
+ *    misrepresented as being the original software.
+ * 3. This notice may not be removed or altered from any source distribution.
+ **/
+
+#ifndef LOVE_SOUND_LULLABY_GME_DECODER_H
+#define LOVE_SOUND_LULLABY_GME_DECODER_H
+
+#ifdef LOVE_SUPPORT_GME
+
+// LOVE
+#include "common/Data.h"
+#include "Decoder.h"
+
+#include <gme.h>
+
+namespace love
+{
+namespace sound
+{
+namespace lullaby
+{
+
+class GmeDecoder : public Decoder
+{
+public:
+
+	GmeDecoder(Data *data, const std::string &ext, int bufferSize);
+	virtual ~GmeDecoder();
+
+	static bool accepts(const std::string &ext);
+
+	love::sound::Decoder *clone();
+	int decode();
+	bool seek(float s);
+	bool rewind();
+	bool isSeekable();
+	int getChannels() const;
+	int getBits() const;
+
+private:
+	Music_Emu *emu;
+	int num_tracks;
+	int cur_track;
+}; // Decoder
+
+} // lullaby
+} // sound
+} // love
+
+#endif // LOVE_SUPPORT_GME
+
+#endif // LOVE_SOUND_LULLABY_GME_DECODER_H