0.3.0

• Updated to Swift 2.2 (Xcode 7.3).
• Made references to class-based subjects weak. This helps to remove subject-machine reference cycles, but it also means you have to keep a strong reference to a subject somewhere else (which you usually already do). When subject references become nil, transitions are no longer performed. Thanks to @bartekchlebek for work on this issue! 👏
• Added default DOTLabel implementation (return "\(self)"). You don't have to change anything. If you have custom DOTLabel implementations, you can keep using them, but if the only thing you do is case Foo: return "Foo", you can safely delete this code.
• Renamed StateMachine<T> to StateMachine<Schema>.