improve readability.php

[adrianjost]

1. https://github.com/andreskrey/readability.php -> no release at the moment, wait for it
2. https://github.com/j0k3r/php-readability - looks like it requires more tools/software on the server -> second choice
3. Buy Code: http://fivefilters.org/content-only/ -> I don't know how good this is and it can't be published here -> third choice