Use function argument instead of mag-menu-custom-options
Update ack-menu to support new mag-menu callbacks

The new mag-menu callback mechanism enables better support for fake
arguments (like the current project directory arg -c), and mutually
exclusive switches. I updated ack-menu to take advantage of this.

I also changed the local project dir arg (-l) to a buffer dir arg (-bd)
and buffer project root dir (-bp) args.