Adds a closure to be called by the default main loop at regular intervals with millisecond granularity.
func will be called repeatedly every
interval milliseconds until it
Continue(false). Precise timing is not guaranteed, the timeout may
be delayed by other events. Prefer
timeout_add_seconds when millisecond
precision is not necessary.
The default main loop almost always is the main loop of the main thread. Thus, the closure is called on the main thread.