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/service-show-response.json

@@ -0,0 +1,20 @@
+{
+    "status": "ACTIVE",
+    "name": "watcher-applier",
+    "host": "controller",
+    "links": [
+        {
+            "rel": "self",
+            "href": "http://controller:9322/v1/services/1"
+        },
+        {
+            "rel": "bookmark",
+            "href": "http://controller:9322/services/1"
+        }
+    ],
+    "id": 1,
+    "deleted_at": null,
+    "updated_at": "2018-04-26T09:45:37.653061+00:00",
+    "last_seen_up": "2018-04-26T09:45:37.649314",
+    "created_at": "2018-03-26T11:55:24.075093+00:00"
+}