adds delegate callbacks for access token and refresh token errors
adds ability to specify auth scope and responseType (defaults to 'code')
adds ability to specify the oauth approval step url. if specified, when that url is loaded an overlay will be placed over the the web view to hide a relatively ugly process. additionally, if specified the library will extract the access code from the loaded approval step page and automatically verify it.
cleaned up some code formatting
enabled ARC
exposes access token class for use in consuming apps - just so consumers only need to worry about one import statement