Correct inaccuracies in docstrings in heso.clj
Turn hesokuri.util/maybe into a macro

Also, remove maybe-restart-agent because it wasn't being used.
Make the hesokuri.heso/start function more testable

Split up into two functions that make it unit-testable. One function simply
returns the send commands used to initialize the sources, and another function
executes the send commands and starts the heartbeats.