*: s/Id/ID/

golang convention dictates that the individual characters in an
abbreviation should all have the same case. Use ID instead of Id.

The protobuf generator still generates code that does not meet
this convention, but that's a fight for another day.
Merge pull request #1051 from bcwaldon/Id

*: s/Id/ID/
etcdhttp: add Peers.Endpoints
main: break out startEtcd func
proxy: introduce director

The director class drives an httputil.ReverseProxy. This is used when
etcd is deployed in proxy mode.
proxy: add proxy-mode functionality to etcd daemon