Add (very) limited support for date-time fields.

Support date-time fields of the form mm-dd-yyyy-hh-mm to the CSV reader.
(I will add more general support at a later date.)

src/csv.m:
src/csv.record_parser.m:
	Support date-time fields.

tests/harness.m:
tests/date_time.{inp,exp}:
	Test the date_time field support.