Flush when optional limit is reached

[alechill]

Optionally limit the amount of actions that can be collated in each heartbeat

Use case:
Collecting actions for sending to analytics, analytics endpoint has a limit of say 50 events in a batch call. Instead of having to maintain a queue wherever the heatbeat is being listened, just beat every interval if less than 50 actions occur, OR when a configured 50 action limit is hit

AC:

• limit?: number option
• If limit reached within heartbeat interval, flush to a premature heartbeat (a murmer???!!), begin interval again (no need to attempt to do this extra heartbeat while retaining overall overall heartbeat cadence)
• If limit not reached withing the normal interval, just behave as usual flushing to a beat beating every x

Not covered

• Not intended to be an alternative to interval, will continue flushing on interval AS WELL rather than acting as a buffer that always waits until limit reached before flushing