More Complete ISO 8601 Date Support

I am trying to handle dates that came in as ISO 8601 format including a time zone offset and having a lot of trouble. Here are two things I expected to work, but did not:

-- Casting to dates with time zone offsets. These results should be different
select cast("2014-09-24T12:29:19 -07:00" as timestamp), cast("2014-09-24 12:29:19 -08:00" as timestamp); 
-- Format string for time zone offset
select unix_timestamp("2014-09-24 12:29:19 -07:00", "yyyy-MM-dd HH:mm:ss Z")

There may be other gotchas around ISO-8601 handling, but those are the two I ran into today.

I also couldn't find documentation on the format string for unix_timestamp, though it seemed to work the way https://docs.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html does other than perhaps time zone and things I've never attempted like era.