Implement ability to list and join peer server networks

[kozbo]

The GA4GH APIs facilitate the interoperable exchange of genomic information but there currently is no way to easily find servers that are supporting the GA4GH APIs as a service. What is needed is a directory service that lists out all participating GA4GH servers. This specification describes a few protocol additions that will facilitate the following capabilities:

• join a list of peers on another service
• report on a list of peers maintained by this service
• return version information about the current server
  This issue tracks the first bare-bones implementation of the peer service specified.
  see schemas; Add ability to list and join peer server networks ga4gh-schemas#760

[david4096]

Closed with #1556