Using gnode for node 0.10 backwards compatibility

Along the same thoughts as discussed in component/duo#118, adding gnode here to get node 0.10 backwards compatibility.

 * also cleaned up the `Makefile` a bit, matching duo-package
 * moved `index.js` -> `lib/index.js` (consistency)
 * added `require('gnode');` at the top of main (the new `index.js`)