Remove Shotgun bullet randomness

[AM-Mikey]

make this a fixed spread, so that it's more fair to the player

[SanpoNeko]

Buff suggested to make the shotgun feels powerful:
+For the first 0.1 second of each bullet lifetime, allow 50% to pierce everytime it contact an enemy. After 0.1 second, it will stop on enemy contact like normal. Need some test to see if this is too OP compared to the sword melee-ranged combat.