return the index of the commited command to the application via do() and add Index func to get the current committed index of the server
return command index in do(); add checking in peer.go; gofmt
Merge https://github.com/benbjohnson/go-raft
we have pass the server pointer to the command, dont need to return index
Merge pull request #32 from xiangli-cmu/master

gofmt and add func to get the committed index