In short: library now can be installed with composer and used with \Fuel\Doctrine::manager(); Configuration options very improved and no need to handle 2 config files anymore. Everything in Fuel db.php
Please see README and pull request for more information. Hope it will be useful :)
Not really, because they're alternatives either you use Fuel models and such or use Doctrine with all it's provided functionality, but I guess you probably could make them both working with same tables only some extra work will be required to configure it so.
When you use Doctrine then similar to Oil functionality is provided by `doctrine` PHP script. ie.
php doctrine orm:schema-tool:create
PS. if you're not familiar with Doctrine then I probably wouldn't suggest using it with FuelPHP