code: function reducePlugins (plugins) {
    var before = []
    var split = []
    var after = []
    plugins.forEach(function (plugin) {
      if (plugin.before) before.push(plugin.before)
      if (plugin.split) split.push(plugin.split)
      if (plugin.after) after.push(plugin.after)
    })
    return {
      before: flow(before),
      split: combineSplitters(split),
      after: flow(after)
    }
  }
docs: Combine multiple plugins into a single plugin.