Rewrote error messages with a consistent structure to explain said errors, as well as a transition to the administrator's contact information. The administrator's information will needed to be plugged in by a more knowledgeable contributor.
Note that because I am not familiar with Go, some of the error messages may have an incorrect explanation for the error. I encourage a double check on the terminology and logic explained in my messages. If there are any errors, please correct the terminology and logic while retaining the sentence structure.
* fix: handle code separately
* fix: option to ignore expiration on id_token and error handling
* fix: op handler as http.Handler
* fix: terminate session possible wihtout id_token_hint
