began to polish up the code

remove $.popup (it was kind of useless at this point, just having
$.fn.popup is fine really)
changed options.addClass to options.popupClass
removed options.destroyOnClose for $.fn.popup, may decide to bring it
back later, not sure yet
also added cursors.html, which doesn't belong here at all, it's just
made it for reference on another project and I already had popups open
in sublime text. I'll move it to a more central location later