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
That's a lengthy discussion... Initially I was thinking that `chr1`... `chrM` would be enough, since the matchmaker protocol is supposed to be used only for humans (in which case an enum would be better than a string). I probably shouldn't be the one to decide this...