List of things to change in v7

• (maybe) PollWatcher: change timeout between intervals to include time spend performing work
• Config: Replace deprecated poll_interval signature with poll_interval_v2
• (maybe) unify all places of panic/error for locking & thread starts
• remove crossbeam
• upgrade mio to 1.0 Prepare notify 7.0 release #560

todo:

• add nightly test with conditional compilation check for Fix build for DragonFlyBSD. #592