Field of View Hook

This should allow mods to manipulate the player's field of view in the same way that movement speed and being underwater affects it. The event is posted whenever the cached FoV value is updated and related attributes are re-calculated.

Rationale: Players are complaining that the runspeed granted by MPS is having too much of an effect on their field of view, and the binoculars no longer work since the value used to calculate it is now rolled into an attribute.