Release 0.8.6

Release 0.8.6 is a minor release and contains bugfixes and new features:

• HierarchicalMachine.add_states will raise a ValueError when an Enum name contains the currently used NestedState.separator.
• Bugfix #486: Reset NestedState._scope when enter/exit callbacks raise an exception (thanks @m986883511)
• Bugfix #488: Let HierarchicalMachine._get_trigger which is bound to model.trigger raise a MachineError for invalid events and AttributeError for unknown events (thanks @hsharrison)
• Introduced HierarchicalMachine.has_trigger to determine whether an event is valid for an HSM
• Feature #490: AsyncMachine features an event queue dictionary for individual models when queued='model' (thanks @jekel)
• Feature #490: Machine.remove_model will now also remove model events from the event queue when queued=True
• Feature #491: Machine.get_transitions and its HSM counterpart now accept Enum and State for source and dest (thanks @thedrow)