Revised ISO 8601 references

Resolved the FIXME's by doing a little research into how ISO 8601
formats are defined.

Also revised all the expires_at and issued_at examples to reference
http://xkcd.com/1179/ which has the handy property of making it clear
which segment is the month, day, hour, and minute.

Change-Id: I81eaf020d2735748a77989fcf494876bd73d814f
Merge "Revised ISO 8601 references"