Call an array of promise-returning functions, restricting concurrency to a
specified limit.
USAGE
import{ callLimit }from'promise-call-limit'// or: const { callLimit } = require('promise-call-limit')const things =getLongListOfThingsToFrobulate()// frobulate no more than 4 things in parallelcallLimit( things.map(thing=>()=>frobulateThing(thing)),{limit:4,},).then(results=>console.log('frobulated 4 at a time', results))