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.

CMakeLists.txt

@@ -136,6 +136,7 @@ add_library(lego1 SHARED
   LEGO1/mxpalette.cpp
   LEGO1/mxpresenter.cpp
   LEGO1/mxscheduler.cpp
+  LEGO1/mxsemaphore.cpp
   LEGO1/mxsmkpresenter.cpp
   LEGO1/mxsoundmanager.cpp
   LEGO1/mxsoundpresenter.cpp
@@ -143,6 +144,7 @@ add_library(lego1 SHARED
   LEGO1/mxstreamer.cpp
   LEGO1/mxstring.cpp
   LEGO1/mxstringvariable.cpp
+  LEGO1/mxthread.cpp
   LEGO1/mxtimer.cpp
   LEGO1/mxtransitionmanager.cpp
   LEGO1/mxunknown100dc6b0.cpp