Basic prototype.

Moving around works, as does unlocking the exit and moving the box to get at the vent.
Added room tracking for snake body

- Game now can track your last <snake length> rooms, in order, and
detect when  you're moving into a room already in this list
- Right now this doesn't happen automatically, to test it out call the
command "testit" after each time you do a room change
- Added debug info for room tracking, use command "debug" to turn this
on
- ctrl-f "TODO" to find work that should be added. Hopefully I can
tackle most of this tomorrow, but I have some other homework to look at
as well.
Inverted the inheritance logic for "snake_room"

Initially I'd set it up so that the room tracking would only occur in
rooms inheriting from "snake_room" but then I realized this was annoying
since almost all of our rooms will probably be snake rooms.

Now, if you want to have some rooms where you can move around freely,
they need to inherit from "not_snake_room", otherwise the room tracking
will still occur in those rooms.
Added grow and clear functions

- still use debug to see output of what's going on
- use test_grow command to grown snake
- use test_clearrms command to reset room track to be "coiled up" in the
current room
- use test_changerms command each time changing rooms to make the room
change logic happen
Automatic room tracking, dead rat and checkpoints

- When changing rooms, rooms now get tracked automatically (don't need
to call a debug command anymore)
- Added dead rat in r22 that you can eat to grow
- Added checkpoint system, so that we can set a checkpoint that the
player will be returned to (coiled up) when they die
Added look ability

Can now look into adjacent rooms and get a message about whether you've
got the snake immediately behind you, seeing its  body, or just its tail
Tech ready

Cleaned up some stuff, inserted some messages, fixed some things.
Prototype tech is now ready and just needs pictures and final writing.
added pictures
Prototype is submit-worthy