Add support for remaining features

[gkjohnson]

trafficstars

• [x] Skinned Meshes
• [x] Understand replaceable textures tables -- See description for skinfamilies and tables in the MDL Wiki
• [ ] Understand bone tables
• [ ] Understand external models
• [ ] Add an eyeball shader for eyes (parameters are defined in the material)

For Animations

• [ ] Need model that comes with animations -- most seem to just be rigged
• [ ] Understand animation blocks
• [ ] Understand animation controllers
• [ ] Understand animation sequences

Low Priority

• [ ] Object attachment points mstudioattachment_t
• [ ] Understand flex descriptions, more -- they're basically morph targets
• [ ] Understand IK Chains
• [ ] Understand mouths
• [ ] Understand pose param descriptions
• [ ] Understand surface prop
• [ ] Understand ik lock
• [ ] Physics mass
• [ ] Understand LOD updates
• [ ] Hitboxes