Minimal changes to API proposal

Delete GetStats, Error() and ErrNotFound and corresponding imports.
Rename Factory.
Replace type Name with DisplayName and remove collection operations (and errors).
    Since the Factory does not maintain a collection, the DisplayName cannot be checked for existence.
    There are no restrictions on DisplayName content.
Add TODOs for missing semantics.
Avoid passing pointers to interface types.
Name return values when necessary.
Add exitStatus return to StartIn().
Remove thread-safe notes--delegate to implementation.
Add DESTROYED state.
Add error return to UpdateCgroups().
Rename Unpause() to Resume().
Add Event subtypes: ContainerStateEvent and OOMEvent.