parking is now a clause of velocity
rename Elevator.Call to Elevator.Hail
use Hail in Car's state
HallSignal#retrieve takes a Hail
HallSignal#arrival now a cast
HallSignal#arrival takes position)
move logic into Hail
whole numbered floors
Hail.best_match tests and improved implementation
inline Hail.create function
flesh out the Hail.best_match function
Hail.add_hail sorts with test
Hail.next has some smarts
Hail.move_toward function
use GenEvent in rider process
wip when 2 calls