Implement event streams instead of callbacks, provide stats collection via a Statter interface
Provide a statter that counts trips and resets for breakers in a panel

Count time spent in a tripped state

Add an event stream and ability to subscribe to a breaker's events. Events are: BreakerTripped BreakerReset BreakerFail BreakerReady

Provide a buffered channel and receive these events.

Have Panel use the breaker event streams instead of callbacks

Have HTTPClient use the breaker's event stream

Remove callbacks from CircuitBreaker

Handle channel creation and buffering ourselves

Remove panel callbacks. Subscribe to breakers if you want events.

Count fail and ready events in panel stats

docs, remove all traces of OnTrip and OnReset

Add some Panel and Panel Stats examples

Remove callback example from README

Closes #16