0.5

• Added support for unsafe conditional requests (If-Match and If-Unmodified-Since headers). Use $util->hasStateValidator($request) to check if the request includes these headers and $util->hasCurrentState($request, $eTag, $lastModified) to check if the request has the current state.
• Added weak ETag comparison for the If-None-Match header

0.4

Removed the public static function CacheControl::fromString to prevent users to call this method on the base class (as this would result in a fatal error since the abstract base class cannot be instantiated). Instead, the fromString method is added to the two implementations: RequestCacheControl::fromString and ResponseCacheControl::fromString.