attack: Separate sneaks and death attacks.
rules.dmgred: Fix missing innate damage reduction.
rules.weapons: Fix ranger dual-wield feat loss if in heavier armors.
attack: Apply parry damage modification to all creatures.
creature.combat: Cache often used functions.

- Modify internal update functions to local.
- Fix incorrect handling of double-sided weapons.
- Fix missing parameter in Rules.GetBaseDamageReduction
effect.creation: Add helper function for creating custom effect types.