server.MemberCount: count peers with len() is cheaper than loop
server.MemberCount: synchronize access to .peers map with mutex
Merge pull request #20 from temoto/patch-1

Patch 1
Merge branch 'master' of https://github.com/xiangli-cmu/go-raft into xiangli-master

Conflicts:
	server.go
Add debug mode.
Add some padding to the entry's commit channel.
Convert LogEntry.result to interface type.
Clear reference to LogEntry.result after return.
Fix TestLogEntryUnmarshal.
Fix TestLogExistingLog.
Clean up Peer.flush().
Log clean up.
Remove s.Peers().
Add s.Peers() and peer cloning.
Remove unnecessary server locks.
Clean up commitCenter().
Remove commitNotify().