Add versioning

[martinbonnin]

Follow up from #39

This introduces versioning to makes it easier to see the latest version of a scalar at a glance. The main index could filter out the outdated versions of scalars.

See also graphql/graphql-wg#1879

[glen-84]

On 2nd thought, perhaps we should wait for the first need for versioning, as opposed to implementing this now. It may not be something that happens often, if at all.

[martinbonnin]

we should wait for the first need for versioning, as opposed to implementing this now. It may not be something that happens often, if at all.

I'd like to push for versioning because it removes friction. It's easy to release v0.1. Releasing v1.0 feels a lot harder.

[martinbonnin]

I've updated the description of this PR to make it only about versionning as it's a separate thing. See #54 for the graphql namespace.

[glen-84]

I'm not following how versioning would make the current index easier to read. The specs should probably just be grouped by author.

[martinbonnin]

@glen-84 you're right, it's a separate concern, I've updated the description. My reasonning is that I don't want to change the index.html too often. I'd rather do everything all at once: versionning + grouping.

Edit: PR for grouping is there: #55

[martinbonnin]

Quick notes from the January Working Group:

@leebyron mentions we already have a graphql namespace, it's the spec, no real need for it.
@benjie says we can do collaborative upvoting. If one scalar is well regarded, other can link to it.
@michaelstaib says we could promote the scalars in the main spec.

@michaelstaib also mentioned we could merge the scalars with the contrib repo