MxSemphore + MxThread + MxThread implementions (#80)

* Add MxSemphore + MxThread and the two implementations I could find
  of MxThread (consumers extend it and override the Run method).

* Implement a function in MxDiskStreamProvider which uses thread and
  semaphore to confirm correct layout / size of those classes.

* All 100% match except two functions with a pair of registers swapped.

LEGO1/mxthread.h

@@ -0,0 +1,57 @@
+#ifndef MXTHREAD_H
+#define MXTHREAD_H
+
+#include "mxtypes.h"
+#include "mxsemaphore.h"
+
+class MxCore;
+
+class MxThread
+{
+public:
+  // Note: Comes before virtual destructor
+  virtual MxResult Run();
+
+  MxResult Start(int p_stack, int p_flag);
+
+  void Terminate();
+
+  void Sleep(MxS32 p_milliseconds);
+
+  // Inferred, not in DLL
+  inline MxBool IsRunning() { return m_running; }
+
+protected:
+  MxThread();
+  virtual ~MxThread();
+
+private:
+  static unsigned ThreadProc(void *p_thread);
+
+  MxULong m_hThread;
+  MxU32 m_threadId;
+  MxBool m_running;
+  MxSemaphore m_semaphore;
+};
+
+class MxTickleThread : public MxThread
+{
+public:
+  MxTickleThread(MxCore *p_target, int p_frequencyMS);
+
+  // Unclear at this time whether this function and the m_target field are
+  // actually a general "userdata" pointer in the base MxThread, but it seems
+  // like the only usage is with an MxTickleThread.
+  MxResult StartWithTarget(MxCore* p_target);
+
+  // Only inlined, no offset
+  virtual ~MxTickleThread() {}
+
+  MxResult Run() override;
+
+private:
+  MxCore *m_target;
+  MxS32 m_frequencyMS;
+};
+
+#endif // MXTHREAD_H