Create browser instance object and return it to the launcher

[gregpabian]

An instance should expose a common API for event and instances life cycle handling.

It should expose:

• stop method that will invoke appropriate API to stop the process (depending on the platform):
  • unix - use process.kill()
  • darwin - use osascript
  • windows - taskkill
• stdout and stderr properties
• pid property
• command property
• args property