Release 0.5.1

This release exposes the Runner type plus its Run, State, and Ready methods.

This allows you to first create a Runner and then Run it (possibly in a separate goroutine) then occasionally check its current State (one of NotStarted, Running, Failed, Stopping, or Stopped)

Additionally, the Ready method returns a <-chan struct{} that is closed with the Runner's underlying Server is ready to accept requests.