SCHEMA: Define associated data with selectors, path components and inheritance

[effigies]

One difficulty with validation is knowing when it is worth making the effort to load an associated file. This meta-schema is intended to hint to validators and other implementations when associations may be relevant.

It could make sense to add filename rules here, as well as indicators of whether a file can be found through inheritance (making some path components optional) or not. For example magnitude images will never be found through inheritance, but must match all entities with their corresponding fieldmap images. bval and bvec, however, can be inherited.

[rwblair]

Looks good! Bval and bvec are pains because they are extensions, so I still need to know implicitly that thats the part of the file name I'm replacing on. But they're the only ones and a legacy rule.

In addition to selectors we could have a target key that lists the desired parts of the filename matched by the selectors to replace. So for events:

target:
  extension: '.tsv'
  suffix: 'events'

The extension along with a boolean for inheritance would let us know how to inherit properly.

[effigies]

Bval and bvec are pains because they are extensions

I think if you implement inheritance logic based off of target, where extensions are included, they shouldn't need separate treatment.