Make sure only one instance is started

This reflects the OpenZWave's Manager singleton and makes it more clear that only one node object has to be initiated.

Author: s0meone

lib/openzwave-shared.js

@@ -48,4 +48,8 @@ addonModule.Emitter.prototype.removeAllListeners = function(evt) {
 	return this;
 }
 
-module.exports = addonModule.Emitter;
+var instance;
+module.exports = function(options) {
+  if (!instance) instance = new addonModule.Emitter(options);
+  return instance;
+}