Create .numberParser()

Create parser generator method called `.numberParser()`

```javascript
var parser = Globalize( "en" ).numberParser();

[ "1", "2", "3.142" ].map(function( x ) {
   return parser( x );
});

// [ 1, 2, 3.142 ]
```

Ref #294
Fixes #296

- [x] Implement
- [x] Docs
- [x] Tests