Schedule work on next tick

[grddev]

If you need to execute something on the reactor thread, or need a simple way to break long-running handlers into multiple steps it would be nice to have a way to execute something at the next reactor tick.

While it is possible to achieve the same effect with short interval timers, I think it makes sense from an API standpoint to separate the two. Also, I'm sure this can be implemented with much lower overhead.