ParseDate parses a value from the date cell. It expects the date to be in
the YYYY.MM form with the exception for October, which uses YYYY.1 format
(presumably Excel drops zero and treats YYYY.MM as s number with up to 2
precision digits... so 1234.10 becomes 1234.1).
Read reads market data in CSV format from the reader. It returns market data
in Protobuf format or error. It is all or nothing operation, i.e., an error
in one of the records invalidaes all data.