Added ability to adjust the number of events the TaskRunner keeps as
there's no way to observe all events otherwise.

Task events differ slightly from 0.8 because 0.9 emits Terminated every
time a task exits instead of only when it exits on its own (not due to
restart or kill).

0.9 does not emit Killing/Killed for restarts like 0.8 which seems fine
as `Restart Signaled/Terminated/Restarting` is more descriptive.

Original v0.8 events emitted:
```
	expected := []string{
		"Received",
		"Task Setup",
		"Started",
		"Restart Signaled",
		"Killing",
		"Killed",
		"Restarting",
		"Started",
		"Restart Signaled",
		"Killing",
		"Killed",
		"Restarting",
		"Started",
		"Restart Signaled",
		"Killing",
		"Killed",
		"Not Restarting",
	}
```