NewCasper create a new instance of Casper argument checkpoints load the checkpoints from leveldb the first element of checkpoints must genesis checkpoint or the last finalized checkpoint in order to reduce memory space the others must be successors of first one.

Casper is BFT based proof of stack consensus algorithm, it provides safety and liveness in theory, it's design mainly refers to https://github.com/ethereum/research/blob/master/papers/casper-basics/casper_basics.pdf.

RollbackMsg sent the rollback msg to chain core.