Merge pull request #21 from fengjingchao/dev

finish simple sendPrepare
add test for recvPrepare, change some func() names in phase2_test
Merge pull request #22 from fengjingchao/dev

rewrite ballot
Merge branch 'dev' of github.com:go-epaxos/epaxos into dev
Merge pull request #24 from fengjingchao/dev

fix ballot compare
Merge branch 'dev' of github.com:go-epaxos/epaxos into dev
update for new ballot, add some comments, change a TestRecvPrepareNoop to TestRecvPrepareNoInstance
change deps from nil to {0,0,0,0,...} when acceptors have no info about the instance
modify some tests' ballot and instance's No. change rejection condition
Merge pull request #23 from yifan-gu/dev

After discussing, agree on merge
fix setting Id in incrementing ballot