The ev module implements an event loop for files and signals.  There's
an implicit global event loop accessible via the [[add]], [[del]],
[[loop]] and [[loopbreak]] functions as well as the support for
manually creating event loop via [[new]] and the methods returned.

Signals can be safely catched and the registered callback is called in
the main code environment, and not in a signal context, so no special
attention is needed.  At the moment, signals can only be handled as
part of the implicit global event loop.

Caveats: if the event A deletes the event B, and the event B is
already pending, it can still be fired once.