菜鸟从零实现raft，仅仅根据raft paper
raft implement by rookie, without referencing any code, just the paper.
built on Mac, prerequests:
- protobuf
- boost/asio
done:
- election
- log replication
- state machine apply and client (interface and an example)
todo:
- snapshot
- reconfiguration
- full tests
- benchmark
- read code: logcabin, braft, hashcorp/raft