docs: def enable_plugin(plugin_name):
      '''
      Enable installed plugin package(s).
  
      Each plugin package must have a directory with the same name as the package
      in the following directory:
  
          <conda prefix>/share/microdrop/plugins/available/
  
      Parameters
      ----------
      plugin_name : str or list
          Plugin package(s) to enable.
  
      Returns
      -------
      dict
          Dictionary containing a flag for each plugin name:
  
           - ``False`` iff the plugin was already enabled.
           - ``True`` iff it was just enabled now.
  
      Raises
      ------
      IOError
          If plugin is not installed to ``<conda prefix>/share/microdrop/plugins/available/``.
      '''
      if isinstance(plugin_name, types.StringTypes):
          plugin_name = [plugin_name]
          singleton = True
      else:
          singleton = False
  
      # Conda-managed plugins
      shared_available_path = MICRODROP_CONDA_SHARE.joinpath('plugins',
                                                             'available')
      # User-managed plugins
      etc_available_path = MICRODROP_CONDA_ETC.joinpath('plugins', 'available')
  
      available_paths = (etc_available_path, shared_available_path)
      plugin_paths = []
      for name_i in plugin_name:
          for available_path_j in available_paths:
              plugin_path_ij = available_path_j.joinpath(name_i)
              if not _islinklike(plugin_path_ij) and plugin_path_ij.isdir():
                  logger.debug('Found plugin directory: `%s`', plugin_path_ij)
                  break
          else:
              raise IOError('Plugin `{}` not found in `{}` or `{}`'
                            .format(name_i, *available_paths))
          plugin_paths.append(plugin_path_ij)
  
      # All specified plugins are available.
  
      # Link all specified plugins in
      # `<conda prefix>/etc/microdrop/plugins/enabled/` (if not already linked).
      enabled_path = MICRODROP_CONDA_PLUGINS.joinpath('enabled')
      enabled_path.makedirs_p()
  
      # Set flag for each plugin: `False` iff the plugin was already enabled,
      # `True` iff it was just enabled now.
      enabled_now = {}
      for plugin_path_i in plugin_paths:
          plugin_link_path_i = enabled_path.joinpath(plugin_path_i.name)
          if not plugin_link_path_i.exists():
              if platform.system() == 'Windows':
                  plugin_path_i.junction(plugin_link_path_i)
              else:
                  plugin_path_i.symlink(plugin_link_path_i)
              logger.debug('Enabled plugin directory: `%s` -> `%s`',
                           plugin_path_i, plugin_link_path_i)
              enabled_now[plugin_path_i.name] = True
          else:
              logger.debug('Plugin already enabled: `%s` -> `%s`', plugin_path_i,
                           plugin_link_path_i)
              enabled_now[plugin_path_i.name] = False
      return enabled_now if not singleton else enabled_now.values()[0]