Adding a helper for getting the beat sent.

Would something like this be helpful?

Usage:

```clojure
(send-beat :in-bus beat-trg-bus :beat-bus beat-cnt-bus :id count-trig-id)
```

I've been playing with beat timing and signals and *guessed* a helper like this might live here?
Since these helpers are all about beats?

I'm finding it very useful to have some global beat event that I can hook devices into.

I could be doing something silly and too bespoke so please excuse my over enthusiasm.