docs: def _load_plugin_entrypoints(self):
          """Load the modules for the psyplot plugins
  
          Yields
          ------
          pkg_resources.EntryPoint
              The entry point for the psyplot plugin module"""
          from pkg_resources import iter_entry_points
  
          def load_plugin(ep):
              if plugins_env == ['no']:
                  return False
              elif ep.module_name in exclude_plugins:
                  return False
              elif include_plugins and ep.module_name not in include_plugins:
                  return False
              return True
  
          self._plugins = self._plugins or []
  
          plugins_env = os.getenv('PSYPLOT_PLUGINS', '').split('::')
          include_plugins = [s[4:] for s in plugins_env if s.startswith('yes:')]
          exclude_plugins = [s[3:] for s in plugins_env if s.startswith('no:')]
  
          logger = logging.getLogger(__name__)
  
          for ep in iter_entry_points(group='psyplot', name='plugin'):
              if not load_plugin(ep):
                  logger.debug('Skipping entrypoint %s', ep)
                  continue
              self._plugins.append(str(ep))
              logger.debug('Loading entrypoint %s', ep)
              yield ep