url: Added support for parsing login options from the URL

As well as parsing the username and password from the URL, added support
for parsing the optional options part from the login details, to allow
the following supported URL format:

schema://username:password;options@example.com/path?q=foobar

This will only be used by IMAP, POP3 and SMTP at present but any
protocol that may be given login options in the URL will be able to
add support for them.