Add a node install packages recipe

__Hello!__

Thanks for this cookbook it was very useful for my needs.

I simply lacked a simple recipe to install node packages quickly via chef configuration. The recipe is pretty basic for now (it only installs node packages globally, and can only specify `version` and `name`)

_Example of usage in a solo run:_
```json
{
  "nodejs": {
    "node_packages": [
      { "name": "bower" },
      { "name": "grunt", "version": "0.4.5" }
    ]
  },
  "run_list": [
    [...],
    "recipe[nodejs::packages]"
    [...],
  ]
}
```

___This was useful for quick provisioning purposes, let me know what you think___
Sure about that ?
maybe you wanted to write something like :
```
      version node_pkg['version'] if node_pkg.has_key?('version')
```