Add support for older PHP 5.x.x versions

This PR adds support for older PHP 5 versions (<5.3.0). Older versions threw the following error when including the main `Soundcloud.php` library file.
 
```syntax error, unexpected T_FUNCTION, expecting ')' in /path/to/Soundcloud.php```

This is also described in [this StackOverflow question](http://stackoverflow.com/questions/9991364/consistent-error-accessing-soundcloud-api-with-php-on-bluehost-server).

The root cause is that `array_map` only supports lambda functions [as of PHP 5.0.3](http://php.net/manual/en/function.array-map.php#example-4772). This PR replaces this method with a simple foreach.