This module implements an event manager that notifies subscribers of keyboard, mouse and resize events received from the termbox API.

Internally, the event manager is managing a NIF-based polling routine and fanning out polled events to subscribers. It works likes this:

1. The ExTermbox.Bindings.start_polling/1 NIF is called with the event manager's pid.
2. The NIF creates a background thread for the blocking polling routine and immediately returns with a resource representing a handle for the thread.
3. When the polling routine receives an event (e.g., a keypress), it sends a message to the event manager with the event data, and then continues polling for the next event.
4. The event manager receives event data from the background thread and notifies all of its subscribers of the event. Steps 3 and 4 are repeated for each event.
5. When the event manager is terminated, ExTermbox.Bindings.stop_polling/0 is called to stop polling and terminate the background thread.

Example Usage:

def event_loop do
  receive do
    {:event, %Event{ch: ?q} = event} ->
      Bindings.shutdown()
    {:event, %Event{} = event} ->
      # handle the event and wait for another...
      event_loop()
  end
end

{:ok, pid} = EventManager.start_link()
:ok = EventManager.subscribe(self())
event_loop()