- make MatrixBase and all expressions aware of their preferred traversal order.

Honor this preference in operator=.
- add several methods to the API
- rework API for diagonal matrices
- add benchmarking code

doc/snippets/MatrixBase_dynBlock.cpp

@@ -1,4 +1,4 @@
-Matrix3d m = Matrix3d::diagonal(Vector3d(1,2,3));
+Matrix3d m = Vector3d(1,2,3).asDiagonal();
 cout << "Here is the matrix m:" << endl << m << endl;
 cout << "Here is m.dynBlock(1, 1, 2, 1):" << endl << m.dynBlock(1, 1, 2, 1) << endl;
 m.dynBlock(1, 0, 2, 1) = m.dynBlock(1, 1, 2, 1);