Output a list of all classes referenced by the given source.

def dependencies(source):
    """Output a list of all classes referenced by the given source."""
    loader = ClassLoader(source, max_cache=-1)
    all_dependencies = set()
    for klass in loader.classes:
        new_dependencies = loader.dependencies(klass) - all_dependencies
        all_dependencies.update(new_dependencies)
        for new_dep in new_dependencies:
            click.echo(new_dep)