Decoupling version numbers of different specifications

[constantinpape]

While working on #46 I noticed that we now need to bump the version number for the HCS spec, although nothing in it has changed. In the future with more specifications for different OME-NGFF formats, this can become pretty confusing, because any change in one of the specifications will require a "global" version bump.

I am not sure if there is a better solution, because having diverging version numbering in the same repository could introduce it's own set of problems. But I still wanted to bring this up for discussion.

[joshmoore]

Agreed. My (strong) preference would be to introduce a single top-level item that provides the version:

{
    "@context": "https://ngff.openmicroscopy.org/contexts/0.2"
}

that would allow for a json-ld parsing: https://json-ld.org/spec/latest/json-ld/#the-context

[constantinpape]

Closed in favor of #83