merge single level defaults over a config object

 A simple one level options merge utility. This module exports
 a function that takes 2 arguments: options and defaults.
 When called, it overrides all of undefined properties in
 options with the clones of properties defined in defaults.
 Sidecases: if called with a falsy options value, options will
 be initialized to a new object before being merged onto.
 .
 Node.js is an event-based server-side JavaScript engine.