Merge pull request #34 from xiangli-cmu/master

add stats
Merge pull request #35 from xiangli-cmu/master

add rpc
Merge pull request #36 from xiangli-cmu/master

add a failure chan to detect instancd failure
add LB remove instance listener
Merge pull request #37 from fengjingchao/dev

add LB remove instance listener
failure channel