clarified the accepted values for temporal
made the iso 8601 links consistent
changed the 8601 hyperlinks to the wikipedia entry

It's more useful, esp. given the advice around durations and such
added ISO 8601 clarications, corrected spelling
removed extra word in temporal
added link for Open XML mime types
Merge pull request #262 from project-open-data/mime-and-temporal-schema-clarifications

Mime and temporal schema clarifications