Move exec and events components to util module

The exec and events components are common components that
are used by both runtime and registry. It makes sense to
move them into the util package.

This also adds some docs to the registry module

packages/node_modules/node-red/lib/red.js

@@ -121,6 +121,10 @@ module.exports = {
     },
     /**
      * Stop the Node-RED application.
+     *
+     * Once called, Node-RED should not be restarted until the Node.JS process is
+     * restarted.
+     *
      * @return {Promise} - resolves when complete
      * @memberof node-red
      */
@@ -161,10 +165,10 @@ module.exports = {
 
     /**
      * Runtime events emitter
-     * @see @node-red/runtime_events
+     * @see @node-red/util_events
      * @memberof node-red
      */
-    events: runtime.events,
+    events: redUtil.events,
 
     /**
      * Runtime hooks engine