Pickadate - great jQuery plugin from
https://github.com/amsul/pickadate.js, http://www.jqueryrain.com/?V4r9LjZ3
Added "expires" field to _items --- when a particular todo item expires. It is a Javascript Date() object or undefined.
attachCallbacks and renderItemHTML now take care of that. In particular, attachCallbacks sets the initial value to the widget and attaches Pickadate.js to the widget.
Added JS and CSS for Pickadate.js widget.
Tinysort now can sort by date using a custom comparison function