Use STTP instead of Akka as the backend

[paulpdaniels]

The current implementation locks us into using the the AkkaBackend. A more flexible approach would be to swap it out to use STTP which has its own backend concept (one of which is Akka). For our purposes we needed such a capability so I created a spike here https://github.com/leadiq/drunk/pull/1 . If the maintainers like the approach I can also open the PR to this repo so it makes it back to the mainline.

[zalbia]

Would love to see this too.