Gen 1: Implement proper Counter mechanics

We now have proper Counter mechanics for Gen 1. It works as follows:
When Counter is selected, after the move hit test and apply damage, it's calculated.
Counter misses if the opponent's last selected move's Base Power is 0.
Counter misses if the opponent's last selected move's type is not Normal or Fighting, or if the move is Counter.
Counter misses if the last move used in the battle did no damage to its target.
If these three tests were passed, damage dealt by Counter will be equal to twice the damage dealt by the last move used in battle.
Counter can still miss due to 1/256 chance.
Last move used by opponent is literal. If the opponent switches, last move used still applies.

Source: http://www.smogon.com/forums/threads/past-gens-research-thread.3506992/