MXS-1220: Fix resource self links

The top level resource self links pointed to the collection instead of the
resource itself. The individual resoures now also have a links field that
contains the self link to the resource. This should make navigation of the
API easier as all objects have valid links in them.

include/maxscale/json_api.h

@@ -65,6 +65,19 @@ json_t* mxs_json_relationship(const char* host, const char* endpoint);
  */
 void mxs_json_add_relation(json_t* rel, const char* id, const char* type);
 
+/**
+ * @brief Create self link object
+ *
+ * The self link points to the object itself.
+ *
+ * @param host Hostname of this server
+ * @param path Base path to the resource collection
+ * @param id   The identified of this resource
+ *
+ * @return New self link object
+ */
+json_t* mxs_json_self_link(const char* host, const char* path, const char* id);
+
 /**
  * @brief Return value at provided JSON Pointer
  *