Added overlayclose, fixes and Tidy up

Added overlayclose option. Default is true but if set to false it will only close on X
Declared missing variables (many were implicitly declared)
Changed  var options = $.extend(defaults, options); to  var option = $.extend(defaults, options); and all variables accordingly.
because it is a duplicate declaration.
Made the JavaScript better formed by fixing minor warning and errors IDE displays. Including missing semi-columns where it should be and commas where it is unnecessary. It is now has no errors at all!
Note: I only updated venobox.js but not the venobox.min.js!!

Hope you like it. :)