NEW: You now dismember heads with headshots and can dismember limbs with certain tools/weapons. A big thanks to drconfused1 for bringing this idea to my attention.
NEW: New version that works with Firearms mod by Mayic.

One hit headshot kills with:

All firearms/bows
Hunting Knife
Iron/Steel Axes
Iron/Steel Picks
Iron Club
Machete
Sledgehammer
Chainsaw
Auger

These Tools/Weapons will dismember limbs:

Iron/Steel axe - dismember limbs
Mechete - dismember limbs
Chainsaw - dismember limbs
Shotgun w/shell - 50% chance to dismember limbs
Shotgun w/Slug - dismember limbs
Blunderbus - 30% chance to dismember limbs

Firearms Edition:

All Guns - One hit Headshot dismemberment
Golden Gun - dismember limbs
M82 (50cal) - dismember limbs
20g Shotgun - 30% chance to dismember limbs
Chaingun (5mm)- 25% chance to dismember limbs
M249 SAW (5.56x45mm) - 25% chance to dismember limbs

FUN FACT: You can now dismember all limbs on a zombie and keep it alive with only its head and torso! It will still bite you if you get near its head!