updates OpenAM class url for Rest documentation and Base On github repository
fixes typo in OpenAM class usage example
adds OpenAM class and pepesmith to usage information
makes OpenAM init raise a ValueError for empty/null openam_url argument, instead of AttributeError
adds token property and makes class methods use it if no token is passed
makes attributes method request the token attributes in JSON
makes authenticate method call the OpenAM's JSON service
makes is_token_valid method use the OpenAM's JSON service
removes the assignment of logout response since it's not used afterward
makes get_cookie_name_for_token use OpenAM's JSON service
makes get_cookie_names_to_forward use OpenAM's JSON service