#5 Allow overriding the mouse position in mousewheel events

Rather than using love.mouse.getPosition() to get the mouse position in mousewheel events, use the getmouse() method which can be user-overriden This allows using Gspot with transformed coordinate systems, by transforming the click position to world coordinates in love.mousepressed()/love.mousereleased() and overriding gui.getmouse() to return world coordinates as well.