Various documentation updates:

- update the tutorial
- update doc of deprecated cwise function
- update cwise doc snippets

doc/snippets/MatrixBase_rowwise.cpp

@@ -2,4 +2,4 @@ Matrix3d m = Matrix3d::Random();
 cout << "Here is the matrix m:" << endl << m << endl;
 cout << "Here is the sum of each row:" << endl << m.rowwise().sum() << endl;
 cout << "Here is the maximum absolute value of each row:"
-     << endl << m.cwise().abs().rowwise().maxCoeff() << endl;
+     << endl << m.cwiseAbs().rowwise().maxCoeff() << endl;