Added reference headers and moved some code.

OndselSolver/DiagonalMatrix.ref.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <memory>
+
+namespace MbD {
+    template<typename T>
+    class DiagonalMatrix;
+    template<typename T>
+    using DiagMatsptr = std::shared_ptr<DiagonalMatrix<T>>;
+    using DiagMatDsptr = std::shared_ptr<DiagonalMatrix<double>>;
+}