- eigen2 now fully enforces constness! found a way to achieve that

with minimal code duplication. There now are only two (2)
  const_cast remaining in the whole source code.
- eigen2 now fully allows copying a row-vector into a column-vector.
  added a unit-test for that.
- split unit tests, improve docs, various improvements.

test/main.h

@@ -114,10 +114,13 @@ class EigenTest : public QObject
 
   private slots:
     void testBasicStuff();
+    void testLinearStructure();
+    void testProduct();
     void testAdjoint();
     void testSubmatrices();
     void testMiscMatrices();
     void testSmallVectors();
+    void testMap();
   protected:
     int m_repeat;
 };