Strict record handling

Hi!
I have the requirement to fail if the records are incomplete. Up to now, fast-csv is quite polite and just consideres an incomplete line as the first field/property and continues.

A workaround wouuld be to check in the validate function if the row is incomplete. but based on the amount of fields, it is very complex to identify a record which may have some fields left empty (which might be valid) and some literally missing.

Therefore introduced a new property (on default, the existing behavior remains unchanged) to emit data-invalid events on incomplete rows.