convert to current mw standard, +code cleanup

@TehKittyCat This works, except the change from a hardcoded description message for Special:Version which doesn't load for me. I'm not sure if it's something caused by my vagrant devbox, so I'll follow it up at a later date.
`$wgRSch`, `$wgRSHiscoreCache` and `$wgRSTimes` don't need to be globals imo, although in the current setup there's not much else available. If this function is split into a separate file, they could be moved to class properties. For example:

```php
class RSHiscores {

    // have a separate cache for each?
    private $hsCache = array();
    private $oshsCache = array();
    private $sehsCache = array();
    // for tracking number of http requests so far
    private $times = 0;
    private $rsch;

    public static function hiscores( ... ) {
        // do stuff here
    }

    public static function osHiscores( ... ) {
        // for old school hiscores
    }

    public static function seHiscores( ... ) {
        // for seasonal hiscores
    }
}
```
PHP isn't my string suit, so I'm not sure if this would work. It just relies on the parser function not generating a new instance of `RSHiscores` with every use.