Advancing Fire Added

Added the ability to use Advancing Fire upon entering enemy-controlled areas. It uses 1-6 HE rounds, and if a battle encounter is triggered, you get an attack on enemy units right after any artillery or air strikes. It can be combined with an arty or air strike as well. Advancing fire affects all enemy units on the map, but is less effective against vehicles, against units at medium or long range, and pins units rather than laying smoke. At the moment the game does not track friendly tanks lost between battles, so it has no effect on advancing fire, but this is definitely an aspect I’m thinking about adding in a future version.