Added middle and right button support.

By default Hammer only supported left-button mouse input.

Now this can be configured by passing in mouseButtons array to Hammer options object like so:

    Hammer(element, {
        // Left, mid and right buttons allowed
        mouseButtons: [0,1,2]
    });

PS: Handle and preventDefault the "contextmenu" event yourself for right-click dragging with Hammer to work properly in your document. Example:

    document.documentElement.addEventListener("contextmenu", function (ev) { ev.preventDefault(); });