Fixed the order of the arguments in #initialize.
start => start!, start? => start; same for stop restart and kill.

Since start? did not return a boolean, it makes more sense to call it
start. Also, since start raised a ServerError on failure, renaming it to
start! made more sense.
Updated the README to reflect the true return type of lifecycle methods.
Minor version bump (1.5.0)

Since the lifecycle methods have been renamed, I think this constitutes
a minor version bump.
Use id as the real docker ID and add attributes repository and tag
Adjust test to user ID (which is unique) instead of repository name