100% Match of MxDSFile (#51)

* 100% Match of MxDSFile

* ...almost, MxDSFile::Open is still not quite matching but all of the
  other methods are 100% matching.

* Turns out that most of the virtual methods and some of the members are
  actually on the MxDSSource base class, which I've pulled out as part
  of this.

* In order to implement the methods I added the MXIOINFO class, which
  seems to be a thin wrapper around the MMIOINFO windows structure. We
  can tell this because MMIOINFO::~MMIOINFO was included in the DLL
  exports, and calls down to a function which deconstructs something
  looking exactly like MMIOINFO.

* Add mxdssource.cpp

* mattkc feedback

* some accuracy improvements

* Use FOURCC macro

* Tirival solve in mxioinfo.cpp

* Update mxdsfile.cpp

0xFFFFFFFF -> -1

---------

Co-authored-by: Christian Semmler <mail@csemmler.com>

LEGO1/mxdssource.cpp

@@ -0,0 +1,14 @@
+#include "mxdssource.h"
+
+// OFFSET: LEGO1 0x100bffd0
+void MxDSSource::SomethingWhichCallsRead(void* pUnknownObject)
+{
+  // TODO: Calls read, reading into a buffer somewhere in pUnknownObject.
+  Read(NULL, 0);
+}
+
+// OFFSET: LEGO1 0x100bfff0
+long MxDSSource::GetLengthInDWords()
+{
+  return m_lengthInDWords;
+}