sop version: add --sop argument to indicate compliance with a particular version of the spec?

I've received reports that reviewers and users don't know what to expect from a sop implementation, other than just trying and checking for errors like SOP_UNSUPPORTED_SUBCOMMAND.

Given that not every version of sop will implement every subcommand or option, i'm also not entirely sure how much sense this proposed semantics makes.

This is also a pretty clunky versioning scheme. Maybe it would be better if sop itself had some sort of semver approach?

I'd be open to other means of reporting intended levels of compliance with the spec, but i wouldn't want to introduce anything particularly fancy.