Adds ponies as a playable civilization.

Ponies come in four varieties, each with different strengths.

• Earth ponies do well at farming, woodworking, and anything nature-related.
• Pegasi do well at military skills, as well as metalworking.
• Unicorns do well at mining, stoneworking, and most crafting.
• Alicorns have a small bonus to every skill, but are much rarer than the other types.

Intended playing style:

• Ponies live in towns, not underground fortresses, so try to build on the surface where possible.
• Ponies are herbivores, so avoid killing animals or fish for resources. Don't enable any of the following labors: bone carving, butchery, fish cleaning, fish dissection, fishing, hunting, leatherworking, small animal dissection, tanning.

The second point is partially enforced by the mod: "tan hide" and a few other reactions are disabled for the pony civ.

Known issues:

• Ponies under a strange mood can still demand bone, shell, or leather. There doesn't seem to be a way to disable this. I've started working on reactions for creating non-animal-based substitutes, but they aren't finished yet.
• Ponies may need some buffs to be more effective in combat (needs more testing).
• Unicorns' skill growth rates may make them slightly overpowered relative to the other tribes.

This mod is based on the pony creature and entity definitions from "My Little Fortress 4.4" by Valikdu: http://dffd.bay12games.com/file.php?id=12181