Add ability to handle wheel events with clog:set-on-wheel

[Aethor]

While working on a project, I needed to capture mouse wheel events. I did not find the needed functions in clog, therefore I rolled my own implementation, which I contribute here.

The wheel event reports the following data: delta-x, delta-y, delta-z, delta-mode (I based myself on https://developer.mozilla.org/en-US/docs/Web/API/Element/wheel_event).

I added a test on the "********" button of test-clog:on-new-window: scrolling the button prints delta-x and delta-y.

[Aethor]

I see that in the documentation, there are only the following types of events: :mouse, :pointer, :touch, :keyboard. I set the type of this event as :wheel, I don't know if this is wise? In that case, we would need to add a new event type section to the documentation.