Updated version number to 1.8.3
Bug fixes and minor updates

- fixed a bug where the plugin would freeze for certain combinations of
disabled/enabled dates; thanks Yogesh;
- fixed a bug where having two paired date picker with "direction" set
to FALSE, the second date picker will not obey this rule once a date is
selected in the first date picker; thanks Shane M;
- fixed a bug where when having paired date pickers, the "Today" button
was sometimes available although it shouldn't have been; thanks Matt;
- fixed a few minor issues reported by JSFiddle's JSHint;
- minor update of source code regarding optimal usage of jQuery for
creating the wrapper around the parent element;