[EN] Create a `start-event-handler!` function.
[EN] Create a `start-event-handler!` function.

We need a way to consistently start (and stop) threads for processing
incoming events. This function takes a handler and a channel and loops
over messages on the channel, passing them to handler. There are two
ways to stop the thread. One is to close the channel. The other is to
call the :stop! function that is returned within the map.

democracyworks/electorate-works