Large cookie Max-Age values can cause a denial of service

Affected versions of this crate use the time crate and the method
Duration::seconds to parse the Max-Age duration cookie setting. This method
will panic if the value is greater than 2^64/1000 and less than or equal to
2^64, which can result in denial of service for a client or server.

This flaw was corrected by explicitly checking for the Max-Age being in this
integer range and clamping the value to the maximum duration value.