Merge pull request #33 from xiangli-cmu/master

Check checksum before load snapshot
Merge pull request #34 from xiangli-cmu/master

clean up promotion
Merge pull request #36 from xiangli-cmu/master

when promoted, election timeout should be stopped
Merge pull request #38 from xiangli-cmu/master

change log ouput format to Lmicroseconds
Merge pull request #39 from xiangli-cmu/server

Blocking the transportation when the server will stepdown
Merge pull request #40 from xiangli-cmu/server

after stepdown candidate should return from collectvote and restart electiontimeout
Merge pull request #42 from xiangli-cmu/server

Server.go refactor
Merge pull request #45 from xiangli-cmu/server

add server state mutex to avoid state race condition
[Fix #47] Clean up external interface.
Merge pull request #48 from benbjohnson/47-external-interface-cleanup

[Fix #47] Clean up external interface.