How do I get the schema document associated with a particular versionof the spec

The RDDL documents are per namespace. For a given namespace there may be
multiple versions of the schema document. Currently the RDDL contains
only pointers to the latest schema. So how do I get to a particular
schema that is associated with a particular spec version.

I suggest that we include links to all the schema files associated with
a particular namespace.

-Anish
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