Add class TBStateMachineSubWrapper.
Renamed wrappers into states.
TBStateMachineParallelState inherits from TBStateMachineState.
TBStateMachineSubState inherits from TBStateMachineState.
Remove TBStateMachineNode protocol fromTBStateMachine implementation.

Protocol method use TBStateMachineState as parameter types now. Implementations of protocol use TBStateMachineState as parameter and respective variable type now.
Update code and unit tests to new sub state wrapper implementation.

Relates to feature #8
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.
Update README.md and CHANGELOG.md
Update podspec.
Update header documentation.
Update README.md.
Update doc.
Update doc.
Merge branch 'feature/substate_refactoring' into develop