The namespace has been changed (ui -> mjs) according to jQuery widget best practices. The file name has been updated accordingly.
It is now possible to define the root items as being protected, i.e. they can be sorted but only as root, and no child che become root.
There is the possibility to define a custom isAllowed function.
Added an option to specify the ID of the root element, default is 'null'.
Small change to the custom isAllowed() function to reflect the english language!
License changed from CC to MIT, to go with jQuery's license