Bug reports: Updating Steady counter rate

I've ran into an issue trying to programmatically update the rate of a Steady counter.

I've wanted to start with emitting no particles and for convenience, I tried to set the rate of Steady to 0 and the increase it at a later time.

However, this causes Steady's _timeToNext to bet set to Infinity, effectively making any further rate changes ineffective.

A similar issue exists with very small numbers, scheduling the next emit so far in the future that rate changes never apply in time.

A work around is to call startEmitter(), which resets _timeToNext and allows the new rate to take effect.

I suggest to reset _timeToNext in the rate setter as well, so that rate changes apply without having to take the extra step.

P.S: Great work you've done with Flint! I really enjoy working with its nice syntax.