Add native String parsing methods

Hello Phil,

please merge the following String parsing methods:

```
<java.lang.Integer: int parseInt(java.lang.String)>
<java.lang.Long: long parseLong(java.lang.String)>
<java.lang.Float: float parseFloat(java.lang.String)>
<java.lang.Double: double parseDouble(java.lang.String)>
```

Thanks!

Martin