Changed map cell character codes.
Removed outdated FIXME.
Improved a Makefile comment.
Documented all blocking requests. I hope.

If any are undocumented, it could cause unfortunate bugs. But at least
the discrepancy between code and documentation should suggest a source
of the bug. Right?

... guys?
Made make ignore error on server `make clean`.

Fixed bug where if you ran `make clean` twice on the server, the
second invocation would produce an error.
Moved responsibilities to the info manager.

The info manager is now responsible for informing player controllers
about updated cells and their movements, rather than the PlayerInfo
process informing the controller directly.
Players can now see other players.

This reveals a bug: players aren't cleaned up when they disconnect.
They stick around forever, cluttering up the map. Join the backlog,
along with all the other bugs.