Add Composer

Please merge this request to allow using your library with PHP dependency manager Composer (http://getcomposer.org/).

The workflow is pretty simple and you need to do it only once. Packagist will take care of updating package versions according to tags in repo:

1. Commit composer.json
2. Register  on packagist website https://packagist.org/ and submit your library https://packagist.org/packages/submit
3. Add Packagist service hook to the GitHub repo https://github.com/phstc/jquery-dateFormat/settings/hooks#packagist_minibucket 

It would be great if you could add a tag to this repo after merging (it will be marked as a stable release on Packagist).