add benchmark of util/stopper
add benchmark of util/stopper

name             time/op
DirectCall-8     2.15ns ± 5%
Stopper-8        1.54µs ± 6%
DirectCallPar-8  0.89ns ± 2%
StopperPar-8     1.11µs ± 9%

glycerine/cockroach,cuongdo/cockroach,petermattis/cockroach,cockroachdb/cockroach,maxlang/cockroach,paperstreet/cockroach,nieyy/cockroach,paperstreet/cockroach,nieyy/cockroach,cuongdo/cockroach,maxlang/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,sunya123/cockroach,sunya123/cockroach,vaibhavarora/cockroach,bg451/cockroach,arjun4084346/cockroach,bg451/cockroach,vivekmenezes/cockroach,maxlang/cockroach,il9ue/cockroach,veteranlu/cockroach,il9ue/cockroach,nieyy/cockroach,il9ue/cockroach,vivekmenezes/cockroach,sunya123/cockroach,vaibhavarora/cockroach,maxlang/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,maxlang/cockroach,arjun4084346/cockroach,sunya123/cockroach,bg451/cockroach,vaibhavarora/cockroach,bg451/cockroach,nieyy/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,paperstreet/cockroach,marcuswestin/cockroach,petermattis/cockroach,cockroachdb/cockroach,petermattis/cockroach,marcuswestin/cockroach,glycerine/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,veteranlu/cockroach,glycerine/cockroach,sunya123/cockroach,il9ue/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,il9ue/cockroach,cuongdo/cockroach,vivekmenezes/cockroach,arjun4084346/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,vivekmenezes/cockroach,cockroachdb/cockroach,marcuswestin/cockroach,cuongdo/cockroach,paperstreet/cockroach,veteranlu/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,nieyy/cockroach,maxlang/cockroach,arjun4084346/cockroach,marcuswestin/cockroach,glycerine/cockroach,glycerine/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,petermattis/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,petermattis/cockroach,arjun4084346/cockroach,cuongdo/cockroach,arjun4084346/cockroach,il9ue/cockroach,glycerine/cockroach,marcuswestin/cockroach,bg451/cockroach,sunya123/cockroach,marcuswestin/cockroach,nieyy/cockroach,maxlang/cockroach,sunya123/cockroach,cuongdo/cockroach,nieyy/cockroach,cuongdo/cockroach,bg451/cockroach,sunya123/cockroach,bg451/cockroach,cockroachdb/cockroach,paperstreet/cockroach,petermattis/cockroach,il9ue/cockroach,maxlang/cockroach,veteranlu/cockroach,marcuswestin/cockroach,cuongdo/cockroach,marcuswestin/cockroach,veteranlu/cockroach,il9ue/cockroach,glycerine/cockroach,paperstreet/cockroach,petermattis/cockroach,vivekmenezes/cockroach,petermattis/cockroach,glycerine/cockroach,nieyy/cockroach