fix logic to wait for executor stop

[hiroebe]

What does this do?

Add stoppedCh aside from stopCh, which is used to wait for the executor to stop

Which issue(s) does this PR fix/relate to?

Resolves #391.

List any changes that modify/break current functionality

Have you included tests for your changes?

No

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes

[hiroebe]

We don't need capacity for this channel. Closing the channel is enough to tell the stop.

[hiroebe]

We need two channels for this use case. In the previous implementation, struct{}{} sent at L123 might be received at L124, which means start() loop never stops.

[JohnRoesler]

something the panic handler test is hosed. i'll try and look at it later - unless you beat me to it 😄

[hiroebe]

@JohnRoesler
I've added a commit to fix the test. 474913e
stop() must be called after the jobFunction has started. Otherwise, jobFunction is never called and the test never finishes.