Allow mocking a tap on given xy-coordinates

[NovapaX]

Currently it's not possible to easily simulate a click / tap on given coordinates.

see also: #93 (comment)

I'd expect to be able to call:
tap(node, xy) like the click function (which is not exposed):

function tap(node, xy) {
    xy = xy || middleOfNode(node);
    // do stuff
}