v2.0.0

• Includes breaking API changes, the new external API is:
  • set(position, duration)
  • start()
  • stop()
  • reset()
• Unbreaks the setTimeout based fallbacks clock.
• Adds checking or arguments, incorrect use should throw exceptions.
• Timer state has been moved to an object to allow for "atomic" updates.
• duration will now be Infinity when counting forever.
• Updated demo and README.