docs: function(initial_store, options) {
      if (store._store_created) {
        throw 'cannot create more than one global store'
      }
      for (let k in initial_store) {
        store._store[k] = initial_store[k]
      }
      if (options) {
        Object.assign(store.options, options)
      }
      store._store_created = true
    }