Add version number as public variable

[Indigo744]

First of all, I really like your library. Good job!

However, it would be good if it provides the current version in a public variable, for instance accessible by $.Zebra_DatePicker.version.

I can think of several use cases for such information:

• allow people to build plugins for a certain version
• check current version and github version for updates

Of course, you will need to remember to modify this variable each time you release a new version.
But I think it is always worth the hassle.

Example of implementation (that I find useful) : DataTables (jQuery plugin):
https://github.com/DataTables/DataTables/blob/master/media/js/jquery.dataTables.js#L9416

I could submit a PR if you want.

Thanks!