scriptSig contains 4 segments: encoded Height (vaired length) + Seqence (4 bytes) + TimeStamp (8 bytes) + Beneficiary str(40 bytes) + Optional（pool tag） only returns height， beneficairy as items[0],[3].

New create a new PowPool instance.

==============APIs for consensus ===================.

Options options for tx pool.

PowBlockEvent will be posted when pow is added or status changed.

PowPool maintains unprocessed transactions.

pow decisions.