What about using interfaces?
Merge branch 'master' into pr/1

* master:
  Fix referencing array parameters by other parameters. Added type
check when concatenating parameters - only scalars can be concatenated.
  Notify service name now can also work with "@" sign in front.
  Fix out of bounds check in parameters resolved.
  Eased access to resolvers in the container.
  Update MD\Foundation dependency to make sure everything works under
HHVM.
  Revert "Fix closure services for HHVM?"
  Fix closure services for HHVM?
  Removed unused use statement.
  Better test coverage.
  Implement container interoperability.
  Docs complete.
  More docs.
  Work on documentation.
  Add newlines at end of files.

Conflicts:
	src/Container.php