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
Richard Durbin <notifications@github.com> writes:
> In src/main/resources/avro/wip/matchmaker.avdl:
> I really think that GA4GH should have a consistent representation for genetic
> variation. Making a different representation in the MatchMaker interface and
> the Variants interface would send a bad message of not being joined up

A big +1 to this.  These kind of inconsistency lead to cascading
complexity and confusion for both the implementation and
consumers of the APIs.