Add NODE_ENV option

I tried to base this on the port option as much as possible.  Here's a
summary of what I've done.

- Added the NODE_ENV option with a default of undefined
- Updated README with option
- Added unit test in `custom_node_env_test.js` (modified the app.js to
  have a configure('production') piece)
- Fixed some jshint pathing that was missing files and fixed jshint
  errors it found.

Feedback welcome if you'd like something altered.