Update for compatibility with Cordova 3.0 Plugman Specs

I updated this simple but fantastic plugin to conform with the Plugman spec, as well as support for Cordova 3.0.

* Method signatures changed
  * Changed methods to handle null strings
Plugin.xml added
Folder structure changed to recommended

Also, are you game for moving this to the official PhoneGap plugins repo?  I think it would make a tremendous addition.  I've tested on iOS 7 and everything looks great.