v6.8 remove rc.go
v6.8.1
Merge branch 'tripod' of https://github.com/zagfox/cse223p
v7.0 add data transfer
v7.1 complete data transfer
v7.2 fix bug in paxos, it is now fast
v7.3 fix bug in paxos, when checking node in responders
v7.3.1 modify TODO
v7.4 modify client to prepare for lock lease
changed everything to interface