Added ability to add callbacks when state is entered or exited.
  * E.g., [sm entering:@"state" do:^(LSStateMachine *sm) { }] and [sm exiting:@"state" do:^(LSStateMachine *sm) { }]
  * Added tests
  * Updated Kiwi to version 1.1.1 (1.1.0 spec had a bug.  See: https://github.com/CocoaPods/Specs/pull/245)
  * Added examples to README.md