This is a backout of what I've done previously. Expiration check is
better done in extraction where a user can optionally specify a base
date.
Add an internal method delete() to delete an existing cookie.
The leading dot itself should be meaningless since there is the second
field to tell if the cookie is issued for a domain and that was the
reason I once removed it, but on second thought it doesn't hurt to put
one.
Fix documents with #each. The uri argument was not made a keyword
argument.
Guarantee that the +uri+ given to AbstractStore#each() is a URI
object.
Make HashStore#each return self as required.
CookieJar#save is the new name for the now obsolete #save_as.
CookieJar#save and #load now accept IO-like instead of a filename.
Change the YAML file format, and make #load discard incompatible data.
