Add licenseListVersion to LicenseExpression

[goneall]

Fixes #131

This adds the licenseListVersion which in 2.3 was at the document level to the licenseExpression.

This is alternative solution to PR #480

[goneall]

After discussing with @swinslow - this seems to be the preferred approach to adding licenseListVersion - changing from draft to "ready for review"

@zvr - please review

[zvr]

I know I'm opening a new topic, but should we be using /Core/SemVer like the specVersion? @swinslow , what do you think?

Totally fine with ignoring this for now and resolving it later in another issue, if it will add delay.

[goneall]

Let's leave it as is for now. Would making it /Core/SemVer less "simple"?

[swinslow]

I'd say future issue (as in "far future"). I think we've always used Major.Minor versioning for the license list and I don't know of any current reason to change it to Major.Minor.Patch.

[zvr]

Well, we used to use SPDX x.y for the spec number till now and we moved to SemVer; it might be ok to do the same here.

If not, we have to add a pattern for the valid values of this string, i.e making sure they match x.y -- and I think we have said that even single instances of patterns should be separate custom datatypes. Definitely more complicated.

But as I said, this might be a different issue and this can be merged.

[goneall]

I agree with @zvr that using SemVer would be simpler than creating a different datatype.

@swinslow - if you're OK with the change, I'll update this PR. If not or if you're not sure, I'll merge this and we can open a separate PR to make progress.

[swinslow]

@goneall I'm fine with switching to SemVer if you're okay with it. I'm just conscious that it likely means changes to the License List Publisher so I didn't want to commit to it if you have qualms about it!

For the time being I don't expect we'd do anything other than x.y.0 releases, so maybe it's not that big of a deal in any case. But yes, I'm fine with it if you both are good with it.

[goneall]

Thanks @swinslow for the quick reply - I committed a change to use /Core/SemVer

@zvr - if you could take one more look and approve, I can merge

[swinslow]

I'd say future issue (as in "far future"). I think we've always used Major.Minor versioning for the license list and I don't know of any current reason to change it to Major.Minor.Patch.