copy multi-threads benchmarks from leveldb
copy multi-threads benchmarks from leveldb

weicao/cascadb,weicao/cascadb,tempbottle/cascadb,tempbottle/cascadb,lilothar/cascadb,li0000/cascadb,BohuTANG/cascadb,li0000/cascadb,lilothar/cascadb,BohuTANG/cascadb