v0.2.0

This is a backwards incompatible update. The following changes are needed:

1. Replace all calls to Alarmist.current_alarms/0 with
   Alarmist.get_alarm_ids/0. This is a hard deprecation.
2. Update all message handling on Alarmist events to expect and use the
   Alarmist.Event.t(). In most usage, this means matching on :id and
   :state and it should simplify the handling functions.

• Updates
  • Simplify the API by completely abstracting away the internal implementation
    with uses the PropertyTables library. This will allow for further internal
    improvements without forcing breaking changes.
  • Align the API for getting alarms with :alarm_handler. This added the
    Alarmist.get_alarms/0 function.
  • Remove a race condition involving the use of alarm descriptions.
    Descriptions are sent to subscribers with the alarm status change
    notification now.
  • Use one timestamp value for all alarms that were set at initialization time.
    This removes the ambiguity of whether an alarm changed a few milliseconds
    after Alarmist start up or was one of the original alarms.
  • Report when alarms are in an :unknown state when no information is
    available. This is useful for the :previous_state field in alarm events.