Add happening modifiers to the simulation

[TechnologyClassroom]

Happenings are random events that happen throughout the world that affect gameplay. Happenings last through an event. Read gamelogic.md to see where happenings fit into the order of the game.

Happing modifiers needs to match pages 5 and 14-19 of the first printing in dicemechanicsim.py. The simulation skips happenings currently.

Some happenings are more complex and involve multiple fights during a scene. Complex ones could be skipped when developing the initial happening framework.