Allow for gas clouds of different types (confusion gas, sleep gas, hallucination gas, etc) by passing an additional argument to create_gas_cloud.

Clouds of sleep gas would immediately have a use in Nazgul and orange dragon breath attacks, which are already described as such. They might also be useful for sleeping gas traps, which would emit an actual cloud of sleep gas. Depending on implementation, the sleep gas cloud could have only a chance of inducing sleep rather than always knocking you out, which could make it tactically interesting to navigate/teleport/etc rather than just getting put to sleep and having the cloud gone by the time you wake up.