Implemented filesystem cache, one and only (see #1415)

you should just store the `content` into a `data` property :

```php
<?php
// ...

class NullCache
{
    // ...
    public function write($file, $content)
    {
        $this->data[$file] = $content;
    }

    public function load($file)
    {
        if (!isset($this->data[$file])) {
            throw new LogicException('Not loaded yet');
        }

        eval('?>' . $this->data[$file] . '<?php');
    }
}