Changes

(#2045)Refactor of sync & adv module, increase code readability and system scalability.
(#2028)RocksDB will be an option for the storage engine in the java-tron. The detail of the Rocksdb is described in this document. (https://github.com/tronprotocol/documentation/blob/master/TRX_CN/Tron-doc.md#471-rocksdb)
You can use RocksDB as storage engine when you want to back up the database without the node application stopped, you can check the usage of Rocksdb engine in the document. It has more tuning parameters for faster-synchronizing block and takes up less disk space when compared with the LevelDB.
The database needs to be reset if the DB engine has been changed, but a tool can be used for converting Leveldb data to Rocksdb data, the instructions about this tool can be found here: https://github.com/tronprotocol/documentation/blob/master/TRX_CN/Tron-doc.md#4714-leveldb-database-convert-to-rocksdb-database-english-verison
Add fast-forward feature and the miss rate of the block can be decreased by setting the forward node.

Notices