support keyword fields.

breaks when `read-keyword` returns nil, e.g. when the keyword field is
empty. is this a special case? or should i set the value in the map, not
in the entry?

clj/clarity/cljs/clarity.cljs

      (keyword name)
      nil)))
(defn typed-keyword [kw owner]
  (om/component
    (dom/input #js {:type "text"
                    :className "field"
                    :value (om/value kw)
                    :pattern "^:(\\w+|\\w+(\\.\\w+)*\\/\\w+)$"
                    :onChange (fn [ev]
                                (when (valid? (.-target ev))
                                  (om/update! kw (fn [o n] n) (read-keyword (.. ev -target -value)))))})))
(defn typed-string [string owner]
  (om/component
    (dom/input #js {:type "text"
    (render [_]
      (dom/div nil
        (dom/span nil "{")
        (om/build typed-keyword (:kw data))
        (om/build typed-string (:str data))
        (dom/span nil "}")))))