Add GET /item/:id endpoint

This new endpoint was so easy to add, it would have been a shame not to
do it. Besides, it makes sense since the reponse from `POST /items`
provided a `Location` header for the newly created item.

src/yohoho/core.clj

@@ -64,6 +64,14 @@
   {:status 200
    :body "Ahoy mate, the ship be sailin' alright"})
 
+(defn get-item-handler
+  [request]
+  (let [id (get-in request [:path-params :id])
+        item (db-get-item id)]
+    (cond
+      (nil? item) {:status 404 :body {:error "Not Found"}}
+      :else       {:status 200 :body item})))
+
 (defn get-items-handler
   [_]
   {:status 200
@@ -101,6 +109,7 @@
   (ring/ring-handler
    (ring/router
     [["/ahoy"     {:get ahoy-handler}]
+     ["/item/:id" {:get get-item-handler}]
      ["/items"    {:get get-items-handler
                    :post {:handler create-item-handler
                           :parameters {:body Item}}}]]