leveldb: add WriteBatch to Batch and define its methods
leveldb: add WriteBatch to Batch and define its methods

no2key/goleveldb,hustbill/goleveldb,btcsuite/goleveldb,ngaut/goleveldb,FactomProject/goleveldb,trigrass2/goleveldb,chai2010/goleveldb,rentongzhang/goleveldb,conseweb/goleveldb,syndtr/goleveldb,zzl0/goleveldb