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/runtime/lib/nodes/index.js

@@ -28,7 +28,7 @@ var context = require("./context");
 var Node = require("./Node");
 var log;
 
-var events = require("../events");
+const events = require("@node-red/util").events;
 
 var settings;