CSV dialect - case sensitivity

[stevage]

I don't have a particular need, but perhaps the CSV dialect should record whether the headings are considered to be case sensitive. Seems to be a flag supported by at least some CSV readers: http://joshclose.github.io/CsvHelper/

Or if not, perhaps the doc should indicate the standard position on case sensitivity, even if it's "case sensitivity of headers is undefined".

(Tiny unrelated issue: too late to change "doubleQuote" to something less ambiguous?)

[rufuspollock]

@stevage great suggestion. Do you want to make a specific suggestion and a pull request?