Update compatibilty with leafo/scss 0.1.*

Update `compass.inc.php` to be compatible with the new scss compiler version.
Update also `composer.json` (#6) and `README.md`.
I think that it will be better to set the version like this: ``>=0.1`` because ``scssphp-compass`` doesn't receive updates often.
This way it will be possible to use ``scssphp-compass`` with newer versions of ``scssphp`` even if ``scssphp-compass`` will be completely abandoned (if it's not yet).