Additional parameters for get_project_tasks

Hey! 
I really like your AsanaAPI wrapper for Python, however I had performance issues, as I had to do manual checking for what's completed and had to get full information for each task one by one (which, as you can imagine, causes lots of network traffic). I found that the API allows to do some checking (completed/not completed) on the server side and that you can expand information by default. I made some simple changes so that those two things can be done through your awesome wrapper. I would be super-happy if you could integrate them to your project!

Cheers,
Igor