Merge pull request #35 from fengjingchao/recovery

Recovery
Update README.md
Update README.md
1. changed receiver's behaviour in terms of ballot, now it returns its own ballot; 2. write something about recvPrepareReply.
Merge branch 'dev' of github.com:go-epaxos/epaxos into dev
almost finish recovery, writing tests
grant commit replies higher priority
add test for receiving commit in recvPrepareReply
add test for receiving accepts in recvPrepareReply
add test for receiving preaccepts, result: union deps and send accepts
change interface of sendPreAccept(), add test for receiving preaccepts, result: union deps and send preaccepts
add test for receiving preaccepts, result: send noop
add test for receiving not enough preparereplies, result: send nothing
refactor proposing phase