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
GRCh38 indicates a sequence reference, but not a gene/transcript set.
You probably mean GRCh38.76, GRCh37.75, etc.
NCBI doesn't have this, so MUST use sub-versioned ID (this is also discussed in PR #126 )