Behavior Changes

• roundrobin: strip attributes from addresses (#4024)
• balancer: set RPC metadata in address attributes, instead of Metadata field (#4041)

New Features

• support unix-abstract schema (#4079)
  • Special Thanks: @resec
• xds: implement experimental RouteAction timeout support (#4116)
• xds: Implement experimental circuit breaking support. (#4050)

Bug Fixes

• xds: server_features should be a child of xds_servers and not a sibling (#4087)
• xds: NACK more invalid RDS responses (#4120)