Feature request: add { allowNewer: true } option

[ronkorving]

This option would allow users to break the semver range, but only by providing a package that is newer than the registered range (not older).

Users could then be greeted by a warning, which would depend on #12.

[stelcheck]

Maybe "warn: boolean" would be better, or "error: boolean". I could see someone wanting to go to a lower version than recommended, for instance.

[ronkorving]

See #12 for warnings. I think I would like the options to be disconnected from warnings. If we also want to allow users to go older, that can be an option in and of itself. I don't mind being very verbose with our options.

[stelcheck]

I see. It might be better to find a unified API for that then...

requirePeer('module', {
  error: [true|false|'newer'|'older']
})

Or something like that maybe?

[ronkorving]

Then I wouldn't know if it would throw or warn. In any case, if we add this feature, I would want it to be absolutely backwards compatible. Too many people use this library now for such a small addition to have such a big impact.