cookies plugin: CookieStore API

The cookie jar is made public. Users can manipulate it outside of the scope of the session.

Session implements:

• #make_jar: returns a cookie jar object, which can be passed in the :cookies option.

Cookie Jar implements:

• get(name_or_options)
• set(name, value) (or set(options))
• get_all(name_or_options)
• delete(name_or_options)

Resolves #374 (closed)