Feature suggestion: Standard ISO/RFC formatters

[Dretch]

I think it would be neat to have Formatter values defined for common formats like RFC 3339, so that these common formats don't have to be redefined in every project that uses them.

Do you think this belongs in purescript-formatters? If so I can send a pull request.

[garyb]

Sure thing, common formats would be good to have.

I don't strictly think RFC 3339 is expressible however, since there are various optional parts to it and such. It can be printed as such, for sure, but the parser won't be able to accept anything but the exact pattern used to print.