Add negatable long-form options

[RoUS]

I didn't see this in the issues lists. One thing I'd like to see is negatable options and flags, something like OptionParser's --[no-]optionname capability.

Is this something considered before and ruled out, never really considered, or is there anyone else that would find this a nice feature?

[denisdefreyne]

Automatically generating [no-] choices definitely makes sense!