Shorten the URL to be used by the user and automatically use the
returned code by the server. The browser is opened on
`http://(bindaddress)/auth`, and redirected to the actual URL. When
the code is returned it is automatically inserted, instead of
requiring a copy+paste.
This is also a workaround for the "open" package, which escapes "&"
wrongly on Windows, so the opened URL's are invalid.
* get rid of depreprecated "code.google.com/p/goauth2/oauth"
* store tokens in config file as before
* read old format tokens and write in new format seamlessly
* set our own transport to enforce timeouts etc
