Use npm package for closure-library

BUG=https://code.google.com/p/traceur-compiler/issues/detail?id=205

Review URL: https://codereview.appspot.com/7972044
Fix issue with npm package.js

The main field should point to a file that can be directly required. With this
change the following should work

  npm install traceur -g

and in your node file

  var traceur = require('traceur');

BUG=None

Review URL: https://codereview.appspot.com/7849048
I forgot to uncomment some code in the last patch
exposing node.js related api
fixing main and git url
ignoring node_modules and not packaging unneeded files
custom readme
readme improvements
more info in readme
fixing name
renaming
0.1.0 adapts readme and exposes nodejs friendly API
file utils are not part of public api
0.1.1 removes file utils from public API
adding runtime path
v0.1.2 exposes traceur runtime path