* Tapping a connector, or the `tap` function, is a syntactic sugar
  feature, that wraps the chaining call to `connect` on the signal
  provided by a `connector` when calling `connect`.

  The given `tapFn` will then be applied with the signals next and
  previous value - which conveniently is provided the other way
  around from the signal function (which is applied with id, prev,
  and then next).

  This is aimed at being a very useful and simple way to _tap_ into
  some signal state that is being changed. Often this technique can
  be used in conjuction with effects, or triggers, to build
  behaviour not just with connectors and events, but also by
  _listening_ to maintained signal state - such as the `db` - in
  independent modules.