client_cookie: Add extended cookie directive parsing

[Dampfwalze]

Because most browsers can correct deviations from standards, many websites are a dumpster fire of nonstandard behavior.

One example are the cookie directives, that control the behavior of such. Some websites completely ignore the case of them and you might find a directive named secure instead of Secure for example.

This PR addresses this, by providing a fallback method, that tries to find them case insensitively. It can also be disabled.