* Allow multiple observations of same entity
Why:
* There may be different probabilities for multiple states of the same
entity.
This change addresses the need by:
* Keeping a list of observations for each entity to check on each state
change of the given entity.
* Adding a numeric id to each observation so that they can be
effectively added and removed from `self.current_obs`.
* Adding a test to confirm functionality.
* fix overzealous indenting
29b62f814f