[timers] Use asap.js
[timers] Add asap license to YUI license
[timers] Add soon._impl back
[timers] Mention asap.js in the module's description
[timers] Explain how the prologue works
[timers] Add HISTORY entry for including `asap`
[timers] Copy-paste asap.js
[timers] Explain the difference in the new implementation
Merge branch 'asap' into dev-3.x