Fix: Delay timings

[vHeemstra]

• Consistent setting of delay.
  • Less than ctx.currentTime: assume relative delay, so add ctx.currentTime for absolute timed instructions.
  • Else: assume absolute timing, so use as-is.
  • Note: When a stream buffer is used, the delay is set using a setTimeout() with delay as number of seconds. In case of absolute delay use, this would not be correct. So maybe never allow absolute delay timings?
• Removed inconsistent returns.
• Some additional cleanup/refactoring.