autoType should infer "TRUE" or "FALSE" as booleans

[bothness]

When working with Excel or Google Sheets, boolean values are by default exported to DSV files as uppercase "TRUE" or "FALSE" strings.

It would therefore seem sensible for the autoType function not to be case sensitive when parsing booleans from strings rather than only accepting lowercase. "true", "TRUE" or perhaps even "tRUe" should become true.

[Fil]

I don't disagree on the all-caps values (and while I see no reason to support tRUe, I think that True could be generated by python). However this would be a breaking change, so we'd have to carefully weigh the pros and cons.

[bothness]

Thanks @Fil. I guess I'll put my own polyfill together for now. Would be great if this could be considered for the next major version.