support the `Option` type.

it's similar to the optional keys, but can be used to wrap any type.

clj/clarity/cljs/clarity.cljs

(defmethod empty-value 'Value [[_ v]]
  v)
(defmethod empty-value 'Option [[_ v]]
  (empty-value v))
(defmethod empty-value 'U [[_ & [[_ v]]]]
  v)
                    (keyword? value) {:type "text", :pattern keyword-pattern}
                    :else {:type "text"}))))))
(defmethod make-typed-input 'Option [m owner {type :type :as opts}]
  (let [[_ type] type]
    (make-typed-input m owner (assoc opts :type type))))
(defmethod make-typed-input 'U [m owner {:keys [type key val]}]
  (om/component
    (dom/select #js {:onChange (update-on-change! m key r/read-string)}