Preserve unknown cookie attributes

[kelunik]

Fixes #2.

Unknown attributes are intentionally only preserved when using fromHeader().

[bwoebi]

Will it also be possible to add custom flags to a cookie (apart from directly using Response::setHeader())? If not, why not?

[kelunik]

Not sure whether we should allow that. I'd have to work for all attributes then and might circumvent validation checks. If we won't circumvent validation checks, we might end up with an invalid CookieAttributes instance. If we validate it, there will be a BC break if we add support for new attributes.

[kelunik]

@bwoebi You can always use Response::setHeader('set-cookie', (string) $cookie . '; customAttribute=XY');

[trowski]

Should we have a method to get the array of unknown attributes?

[kelunik]

@trowski No, as any usage of that method will break once support for the used attribute has been implemented.