Various documentation updates:

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

doc/snippets/Cwise_plus_equal.cpp

@@ -1,3 +1,3 @@
-Vector3d v(1,2,3);
-v.cwise() += 5;
+Array3d v(1,2,3);
+v += 5;
 cout << v << endl;