Addition of equivalence associations between Learning Standards

As identified by the Assessment Work Group (AWG), some education agencies are seeking to allow learning standards to be "mapped" to other learning standards, in relations of equivalence.

This is designed to allow the confusion created by the co-existence of several sets of "canonical" overlapping standards at the local level, such as state standards, local standards, and Common Core State Standards.  Allowing the assertion of relations of equivalence is important to agencies trying to draw conclusions on student performance that is indexed to different standards.

See AWG use case: https://techdocs.ed-fi.org/display/GOV/Assessment+Domain+-+Cross+Referencing+Learning+Standards+Use+Case+-+Version+2-26-2019 (note this link may be volatile; consult AWG resource if the document is moved)