Simple Stack 0.9.1

Simple Stack 0.9.1 (2017-02-09)

• _BREAKING CHANGE(!)_: BackstackDelegate has a new method which must be called: backstackDelegate.onDestroy()
  Not calling backstackDelegate.onDestroy() will most likely result in memory leak, so please make sure you call it paired with onCreate().
• BREAKING CHANGE: BackstackDelegate.clearStatesNotIn() is no longer public, because it is automatically managed on state change completion.
• ENHANCEMENT: Added Backstack.CompletionListener which listens to when backstack has completed a state change.
  Added Backstack.addCompletionListener() and Backstack.removeCompletionListener() methods.
  The backstack keeps a strong reference to your completion listener, so make sure you remove your change listener when no longer needed.
• ENHANCEMENT: It is no longer the responsibility of the StateChanger to call backstackDelegate.clearStatesNotIn().
  The BackstackDelegate registers itself as a CompletionListener, and therefore it can call clearStatesNotIn() automatically.
• ENHANCEMENT: Added flow-sample changed to use Simple-Stack, as name simple-stack-flow-masterdetail.