Fix ParallelStates not reacting to global triggers

[TdXYZ]

Fixes issue #48

[Inspiaaa]

Hi @TdXYZ,

Thanks for the fix to the ParallelStates class not reacting to global triggers, and for including the unit tests! I really appreciate your contribution.

I will merge your PR shortly.

Regarding the potential issue you highlighted in #48 that a ParallelStates state may exit during iteration - meaning that the trigger is called on states that are no longer part of the active hierarchy -, I think I have found a solution. I am going to implement it before releasing the next version of UnityHFSM 👍