Add warning when a subclass doesn’t call super on pushViewController:animated:

This method is used for keeping an internal state, so calling super is mandatory.
Allow setting delegate different than self
Using __weak isn’t needed when setting delegates
Merge branch 'add_delegate_forwarding'
Better name for the property indicating the push animation state
Change „Usage“ to „Demo“ in README
Improve comments
Improve code quality in the example project
Release 1.1