This directory contains all rooms in the map. Most of them are generated only
to be loaded, and then removed. The name of a map room is "mX_Y.c" where
X and Y is the coordinates.

This technique makes it possible for find_object() to use the internal hash
table to quickly find rooms.

All these rooms will self-destruct at clean_up() if they are empty.

Look at /doc/mechanisms/map for more information.
