Updated container to run exec commands.
Example usage added
Updated Return codes
Updated exec to use id param
Updated example
Added Test for exec and execstart
Moved options to it's own variable at the top of the test
Merge branch 'add-exec' of github.com:jasonwatt/dockerode into jasonwatt-add-exec

Conflicts:
	lib/container.js
Merge branch 'jasonwatt-add-exec'