matrix storage order can now also be row-dominant (choosable for each matrix separately)

map() moves from MatrixBase to Matrix
much more documentation/examples/snippets

doc/snippets/MatrixBase_diagonal.cpp

@@ -0,0 +1,4 @@
+Matrix3i m = Matrix3i::random();
+cout << "Here is the matrix m:" << endl << m << endl;
+cout << "Here are the coefficients on the main diagonal of m:" << endl
+     << m.diagonal() << endl;