Resolves #64, usage and help

```javascript
nconf.argv({
  "p": {
    alias: 'port',
    describe: 'Port the server should listen on',
    demand: false
  }
}, 'Usage: $0')
```

```javascript
if (nconf.get('help') || nconf.get('h')) {
  return nconf.stores.argv.showHelp()
}
```