Project Bookmarks, and Project Starting and Stopping

As mentioned in #61, I want to get some feedback, etc. Basically, the code I have right now is spike quality (works, is untested, and is ugly). I've noticed that projectile has some different design qualities than other elisp projects I've seen, and I want to check in before continuing. 

Is there a reason projectile has no hooks anywhere? I used some in the design of this branch.

Do we want to let users opt out of having project bookmarks saved? This would also influence certain design choices.

Besides these, I would say check out the code to get a feel for how it works, and also notice the change I made to projectile-project-root.

Thanks, 

Joel