Finished implementing changes as requested by the powers-that-be.

* Changed "disabled_writes" module's name for "module_logging". There
you can disable writes in general or just debugging info (mainly
A*-related stuff).

* Add a "debug_nl/0" predicate, to signal that the newline being entered
is for debugging purposes.

* Reworked memory framework. Now it tries to remember anything it sees,
from agents to inns. The agent also maintains consistency of the
database by revoking e.g. a treasure's known position when it's seen in
an agent's backpack or when it walks past its position and it does not
see it.

* Reworked A* search algorithm to return the cost of the selected path,
letting the agent decide whether to take it (agent_template:execute/3)
or not.