netty transport: add ssl support.
netty transport: set access levels of inner classes properly.
Merge pull request #132 from m1ch1/ssl

netty transport: add ssl support.
Change the cluster configuration of AckProcessor at correct time.
Fixed the bug and more logging messages for AckProcessor.
Merge pull request #131 from EasonLiao/ack_cluster_config

Change the cluster configuration of AckProcessor at correct time.
Add RollingLog implementation.
Merge pull request #133 from EasonLiao/rolling_log

Add RollingLog implementation.
Separate directory for each SyncProposalProcessorTest
Merge pull request #135 from EasonLiao/fix_sync_test

Separate directory for each SyncProposalProcessorTest
Merge leading/following callback with ClusterChange callback.
Merge pull request #134 from EasonLiao/callback_change

combine clusterChange and leading/following callbacks?
Take snapshot in broadcasting phase and use snapshot for recovery.
Merge pull request #136 from EasonLiao/snapshot

Take snapshot in broadcasting phase and use snapshot for recovery.
Use snapshot file for synchronization.
Merge pull request #137 from EasonLiao/snapshot

Use snapshot file for synchronization.
Modify transport to support snapshot file transferring.
Merge pull request #139 from EasonLiao/snap_transport

Change the interface of transport.
Change xid and epoch of Zxid from 4 bytes to 8 bytes.
Fixed cluter_config format.