pointerdown, pointerup events support

[Inversion-des]

Hi!

When I tried to make a trigger for the tap event (for Ractive on-tap with ractive-events-tap plugin):

$.fn.r_trigger = (event_name, opt)->
    el = @[0]
    return if !el
    switch event_name
        when 'tap'
            if win.navigator.pointerEnabled
                simulant.fire(el, 'pointerdown', opt)
                simulant.fire(el, 'pointerup', opt)
            else if win.navigator.msPointerEnabled
                simulant.fire(el, 'MSPointerDown', opt)
                simulant.fire(el, 'MSPointerUp', opt)
            else
                simulant.fire(el, 'mousedown', opt)
                simulant.fire(el, 'click', opt)
        else
            simulant.fire(el, event_name, opt)
    @

I encountered a problem that Simulant fails to fire some events in the legacy mode.
So I had to add 4 events pointerdown pointerup MSPointerDown MSPointerUp to the the eventTypesByGroup.Event

I'm not sure if it is the best way to resolve the problem, so I didn't do a pull request.

Thanks for the lib!