autoScroll: allow settings autoScroll options

interact.autoScroll(options)

where options's properties are
 - margin: distance in pixels the mouse must be for autoScroll to be
   triggered
 - distance: the distance the window is scrolled by in each axis
 - interval: the time in milliseconds between each scroll of distance

Also use a capital s in autoScroll consistently
demo: separate html, css and js files
Don't try to style the cursor of `document`