This PR attempts to fix #669 by reworking how the killFunc is signalled that a shutdown has been requested.

Instead of reading directly from e.binStopCh (that creates a data race with the writer) it closes on a returned shutdown channel that is used from a new mutexed e.stopBin() func. The shutdown channel takes a channel of int, where the int is the "exit code" passed back to the requestor. It isn't actually the exit code of the process, but a code that can be (and currently is) used to os.Exit the entire process if shutdown failed.

The atomic.Bool change is unrelated to the actual issue, but was required to be able to run the unit tests with -race to detect if there were any races between all the channels and goroutine handling going on in this code.

Reading through the issue list there is a good possibility that this PR will fix, or considerably reduce, the problems seen in #640 #492 #334 and do away with the need for #131 .

This PR has been unit tested and development tested on wsl2 linux and an Apple M2 MBP.