Initial Alloy implementation.

This is a regression in functionality and performance, but a much better
foundation for the future of the project (I think). It can run basic
apps under an SSA interpreter but doesn't support some of the features
required to do real 360 apps yet.

src/xenia/apu/audio_driver.h

@@ -21,14 +21,14 @@ class AudioDriver {
 public:
   virtual ~AudioDriver();
 
-  xe_memory_ref memory() const { return memory_; }
+  Memory* memory() const { return memory_; }
 
   virtual void Initialize() = 0;
 
 protected:
-  AudioDriver(xe_memory_ref memory);
+  AudioDriver(Memory* memory);
 
-  xe_memory_ref memory_;
+  Memory* memory_;
 };