Introduces Cli object and Room object, moves kills to Player

So thinking about it more generally, a game's identity isn't made up of
how many *kills* there are, but rather what player is playing it. It's
always important to look at the initialize method to see what parameters
it looks for. The stuff in the initializer should be *things this object
couldn't exist without, i.e. things that represent its identity*.

A game also has many rooms in it, which match up a monster with the
current game's player. I codified the idea of a Room as its own object,
which has a reference to a player, a monster, and the game that it's for.

Now that I realized that a Game's identity isn't its kills, the natural
place to put kills is on a *player*. Now, when a monster dies, it updates
the room's player's kill count and tells the game to start a new room.