Engine Core, Airlock, Endstates

Add the engine core, with the capacity to eject it. It doesn't, though,
disappear from engineering and can be re-ejected.
Finally got a system set up for multiple end states. A game-level
variable called endState can be modified by the return of any
interaction function of any actor that isn't describing, taking, or
dropping. If that gets modified, the game jumps out of the main loop and
into and endState checking area. Right now, it will restart if you walk
out the airlock. Otherwise, it will end. Need to build in an epiloguer.
Modified the corridor and engnieering descriptions.
Add occupy, eject, open verbs