* [ISO8601,SC] Separated the codebase into various modules: date, time, date-time, time interval, generic.
* [ISO8601,SC] Improvements to argument handling of the entire codebase: time, date, utv, utc-time, date-time compounds.
* [ISO8601,SC] Reimplemented the UTC correction/designation of time.
ISO8601 is done!

* [ISO8601_DATE_TIME,NEW] Added iso8601_date_time//3 aggregate DCG rule.
* [ISO8601_TIME_INTERVAL,SC] Unified the code for time intervals.
* [ISO8601_TIME_INTERVAL,NEW] Added support for recurring time intervals.