Preserve context information in the CSV reader output.

For error-reporting purposes it is useful for context information from the CSV
data stream to be available to the client.

src/csv.m:
	Store the stream name in the csv/0 structure.

	Store the corresponding line number in the
	a csv.record/0 structure.

	Do the same for raw_record/0.

src/csv.raw_reader.m:
src/csv.record_parser.m:
src/csv.typed_reader.m:
samples/csv_ex.m:
tests/harness.m:
	Conform to the above change.