New version v1.1

This is a minor mod that adds additional small internal organs to all standard vertebrate creatures, organs made of skin, causing them to yield more leather upon butchering. In addition, the type of leather obtained as well as the number of skins varies depending on the creature size, but follows this approximate scale:

The quality and value of the leathers progresses as (from lowest to highest):

tanned skin - equivalent to vanilla leather, scaled vertebrates (like cave crocodiles) will not yield this leather (VALUE:1)
leather - slightly better protective properties than tanned skin, equivalent value (VALUE:1)
scaly leather - slightly better protective properties than normal leather, particularly to edged attacks. Scaled vertebrates yield this instead of normal leather (VALUE:1)
hide - significantly better armor material than vanilla leather (still worse than wood), only obtainable from bigger animals. (VALUE:2)
tough hide - best armor quality, roughly equivalent to wood. Only obtained from truly massive beasts (elephants, rhinos, ect.) (VALUE:3)

All of these materials are treated as leather and are used by your dwarves for leather reactions.

This mod creates small internal organs made of skin in order to obtain the additional skin layers for tanning into leather (or skin/hide). These organs cannot be targeted by edged attacks in combat, but can be hit by blunt attacks. The small size of the organs and the restriction to one location in the body helps keep them from be involved in combat except rarely, so the effect on creature survivability is minimal.

This mod alters the b_detail_plan_default.txt and body_default.txt raws, so if you currently are using another mod that also edits those raws then you could experience a conflict.

Version 1.1 Change Log:
- Reduced the number of max leathers from 7 to 5
- Rescaled the body sizes for the additional leather yields
- Reduced size of new internal organs to further limit interaction with combat
- Changed leathers to include three different types with improving quality, based on creature size
- Changed STANDARD_MATERIALS_TEMPLATE to cause skinless (i.e. scaled) vertebrates to yield scaly leather
- Removed all modifications of material_template_default.txt to minimize compatibility issues