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
hmm. in the metadata api i had to [add GASex](https://github.com/ga4gh/schemas/pull/136/files#diff-75c9725afa4674cda0108881d2dd2426R12) - maybe I should move that into common.avdl and we'd share it?

take a look and let me know what you think.