add $data parameter to get function

Adds get params as `$data` array to the get function, like this:
```Pest->get('url', array('id' => 1));```

This is the same idea as with https://github.com/educoder/pest/pull/11 but with a few fixes: If the `$data` array is set and the `$url` already contains parameters, the `$url` parameters are replaced.