'Register the extension\'s components in the extension :class:`Registry`.
For example, to register a backend::
def setup(self, registry):
from .backend import SoundspotBackend
registry.add(\'backend\', SoundspotBackend)
See :class:`Registry` for a list of registry keys with a special
meaning. Mopidy will instantiate and start any classes registered under
the ``frontend`` and ``backend`` registry keys.
This method can also be used for other setup tasks not involving the
extension registry.
:param registry: the extension registry
:type registry: :class:`Registry`'

def setup(self, registry):

    raise NotImplementedError
