First commit of the matchmaker APIs

This is a wip translation of the matchmaker APIs into avro.

Autogenerated docs are here: http://cassiedoll.github.io/matchmaker-staging.html
we could make it an enum?
or, we could leave it as a bool, and whenever something else is needed update the field type. (i'm sure the whole api will need versioning at some point just like the rest of ga4gh)

an enum like {observed, not_observed, suspected, etc} is def possible though - lemme know.