Some new features and fixes:

• Make the process of install snapshot strictly sequential. Additionally, add BufferedSequentialReadFileAdaptor and BufferedSequentialWriteFileAdaptor for users to implement byte stream snapshot more easily.
• Store high-frenquency status of Replicator in a sperated structure, to reduce the lock contention with |_send_entries|.
• Fix some cases that leader lease rejects vote or transfer leader.
• Some other bugfix.

fix the compile problem of v1.1.0 with gflag

Some new features and fixes:

• Leader lease to detect if a leader is valid or not.
• LevelDB based meta storage, to merge random IOs caused by small votefor files.
• IO metrics and logs for tracing slow raft AppendEntries requests.
• Fixes for truncate suffix and snapshot load corner cases.

fix some typo and brazel compile problem.

2019-04-26

• Bug Fixes:
  • Fix the compatibility problem with glog and gflags.

first release version.