CookieJar.new: Pass the store class via a :store keyword.
Improve documentation.
MozillaStore: Add #filename, #close and #closed?.
Use the cookie creation time as base time for Max-Age.

Now #expire returns created_at + max_age when expires is nil.

Cookie.parse: the :date keyword is renamed to :created_at, and the
value is set to in parsed cookies via #created_at.

In YAML serialization, #max_age is stored.
Use :memory: database to save test time.
Bump VERSION to 1.0.0.pre4.