2009-02-14  (0.1) Initial Release
2009-02-14  (0.2) Switch to Tom Corwine's yubikey PHP auth method
2009-02-16  Change error message to match standard username/password error
            Update README/INSTALL files
2009-02-17  (0.3) Add option to add separate input box for OTP
2009-02-19  (0.4) SECURITY: Authenticate given OTP in preferences to prevent future use
2009-03-12  (0.5) Add ability to enter a backup yubikey id
                  Update OTP detection logic to permit the use of a Yubikey in static mode
2009-03-21  (0.6) Add custom service api url support
2009-03-21  (0.6.1) Update error detection and notification
2009-04-03  (0.7) Update plugin based on feedback from Squirrelmail devs
2009-05-02  (0.8) Update plugin based on additional feedback from Squirrelmail devs
2009-05-02  (0.8.1) A few last updates
2014-03-28  (1.0) Fix security issue that allowed any valid Yubikey
            to log in instead of only that stored in user preferences.
            Relax PHP requirements (was 5.2.0) (date function fixes).
            Turn off required checkbox when all Yubikeys are removed.
            Clarify configuration settings.
            Allow configuration file to be stored in main SquirrelMail
            configuration directory.
            Add debug setting.