Access to CSV file column headings for import.

[davidkellerman]

For the raw import() method, it would be really useful to have access to the column headings that were present in the CSV file. For the use cases where I've been using the raw import, the column names are what direct the further transformation of the data. (The only way to get them now is to extract property names from the imported records, and, since null properties are omitted from the records, this is problematic.)

Two possible approaches: (1) another event, say header.csv, that provides the header fields; (2) add a header property to the records array returned by the import. I prefer (2) – simpler to code and use – but some may have ethical objections to adding non-array properties to JavaScript arrays.