Update code and unit tests to new sub state wrapper implementation.

Relates to feature #8
Merge branch 'feature/substate_refactoring' of github.com:tarbrain/TBStateMachine into feature/substate_refactoring

Conflicts:
	Pod/Classes/TBStateMachineSubState.m
Add TODOs to unit tests.
Update unit tests.

Enhanced TBStateMachineSubState tests.
Cleaned up TBStateMachineState tests.
Set first state as initial state in TBStateMachine.
Added enter and exit calls in TBStateMachineSubState.
Add event handling logic to TBStateMachineSubState.