Added \floor, \ceil, and \action commands.
Continued standard semantics.

* Defined the types "Wumpus" and "Agent".
* Defined daylight function "light".
* Defined Wumpus and Agent behavior.
Defined \degs (degrees) command.
Defined agent body and percepts.

* Defined the agent's local percepts (agents/wumpuses/... on the same
cell) and the 90° sight cone extending in the direction into which the
agent is looking.