Various documentation updates:

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

doc/snippets/MatrixBase_select.cpp

@@ -1,6 +1,6 @@
 MatrixXi m(3, 3);
-m << 1, 2, 3, 
-     4, 5, 6, 
+m << 1, 2, 3,
+     4, 5, 6,
      7, 8, 9;
-m = (m.cwise() >= 5).select(-m, m);
+m = (m.array() >= 5).select(-m, m);
 cout << m << endl;