Adding an optional user ID and rearranging the "clipit_user" cookie

* Re-arranging cookie to minimize the cookie length,
* Use named subpatterns in regular expression/REGEX:  /(?P<name>\w+)/
Updating the README - optional user ID

* Goes with previous commit,
* Note, the last commit wasn't backwards compatible.
Fixes and improvements from real-world usage - public "get" utilities

* Use: WordPress - JuxtaLearn Tricky Topic Tool
* $this->authenticate(), ->get_user_login()