use rspec local + guard-rspec failed_mode
fix occasionally failing tmux spec
make guard synchronous

  * Guard.start + Guard.stop basically form a "main" loop

  * no "preserved state"

  * "no interactor" means interactor in interruptible sleep() mode

  * give Pry some time to start

  * use Queue to respond to changes in main Thread

  * handle signals asynchronously
move Guardfile reevaluation to runner
continuously run tasks until no more changes
ignore changes not matching any watch() regexp
fix #571 by implementing guard action queuing