Uncovered bug in command matchers that caused attempted matches to throw exceptions and abort matching. Matchers must be able to handle the case where there is nothing left to match and return 0 matches if appropriate. -- Implemented doors. Doors can be open or closed; if closed they cannot be passed through. Create a separate mud object for doors so their state is shared between the connected rooms. No open or close command yet. -- Added a door to the demo area.