Async Hooks API

before(asyncId) and after(asyncId)

{ id: 2, type: 'Timeout', triggerAsyncId: 1 }
{ id: 3, type: 'TIMERWRAP', triggerAsyncId: 1 }
{ stage: 'before', id: 3 }
{ stage: 'before', id: 2 }
'User callback fired'
{ stage: 'after', id: 2 }
{ stage: 'after', id: 3 }