Add API Reference for Watcher

This patch set adds API Reference along with some
fixes to documentation. It partially fixes bug #1757423.

Change-Id: I107b4fd5daf40aad63fc13864debbbbc82a9826c

api-ref/source/samples/goal-show-response.json

@@ -0,0 +1,19 @@
+{
+    "efficacy_specification": [],
+    "name": "saving_energy",
+    "links": [
+        {
+            "rel": "self",
+            "href": "http://controller:9322/v1/goals/6f52889a-9dd4-4dbb-8e70-39b56c4836cc"
+        },
+        {
+            "rel": "bookmark",
+            "href": "http://controller:9322/goals/6f52889a-9dd4-4dbb-8e70-39b56c4836cc"
+        }
+    ],
+    "uuid": "6f52889a-9dd4-4dbb-8e70-39b56c4836cc",
+    "updated_at": null,
+    "display_name": "Saving Energy",
+    "created_at": "2018-03-26T11:55:24.365584+00:00",
+    "deleted_at": null
+}