docs: function createModel (namespace) {
    const model = (namespace) ? { namespace: namespace } : {}
    model.models = {}
    model.reducers = {}
    model.effects = {}
    model.subscriptions = {}
    model.state = {}
  
    return {
      start: function () {
        return model
      },
      state: function (value) {
        mutate(model.state, value)
      },
      reducer: function (key, value) {
        model.reducers[key] = value
      },
      subscription: function (key, value) {
        model.subscriptions[key] = value
      },
      effect: function (key, value) {
        model.effects[key] = value
      }
    }
  }