Nat

I've left all the commits separate, but I'll squash them once you're happy with the review. Thanks for your time!

I also noticed that `NpmSpec` would probably accept `v>0.1.2` as valid. I get that `v` isn't part of semver, but not sure if `>v0.1.2` is preferred or neither. Happy to...

@pgampe Refer to the linked issue. The maintainer is waiting on clarification from the NPM semver implementers. If you'd like action here, I'd be happy for any progress in pushing...