Note: the default expiry time should be the "the latest representable
date". However, DateTime::from_timestamp(NumericLimits<time_t>::max())
isn't feasible due to the for-loops in LibC's time_to_tm. So instead,
this just sets the date to the maxium year.
This adds storage for cookies that maye be set via 'document.cookie' in
JavaScript or the Set-Cookie HTTP header. For now, it parses only the
name-value pair from a set-cookie line, but does not parse optional
attributes.
Currently, storage is ephemeral and only survives for the lifetime of
the Browser instance.
