docs: def find_thirdparty_marshaller_plugins():
      """ Find, but don't load, all third party marshaller plugins.
  
      Third party marshaller plugins declare the entry point
      ``'hdf5storage.marshallers.plugins'`` with the name being the
      Marshaller API version and the target being a function that returns
      a ``tuple`` or ``list`` of all the marshallers provided by that
      plugin when given the hdf5storage version (``str``) as its only
      argument.
  
      .. versionadded:: 0.2
  
      Returns
      -------
      plugins : dict
          The marshaller obtaining entry points from third party
          plugins. The keys are the Marshaller API versions (``str``) and
          the values are ``dict`` of the entry points, with the module
          names as the keys (``str``) and the values being the entry
          points (``pkg_resources.EntryPoint``).
  
      See Also
      --------
      supported_marshaller_api_versions
  
      """
      all_plugins = tuple(pkg_resources.iter_entry_points(
          'hdf5storage.marshallers.plugins'))
      return {ver: {p.module_name: p
                    for p in all_plugins if p.name == ver}
              for ver in supported_marshaller_api_versions()}