Blender Git Loki

Rigify:
- Added two driven-shape-key rig types that create and drive shape keys on a mesh/meshes based on the distance or rotation difference between two bones.
- Fixed bug in finger curl rig type where secondary finger controls were not created. Finger type can also now (optionally) have a hinge switch (useful when using it for wings).
- Changed the blending system in rigify_utils to use copy_transforms constraints instead of copy_loc+copy_rot.
- Finished the quadruped leg type. Now has both ik and fk control and ik/fk switching. Also uses a rotating bone to control the knee direction instead of a pole target (seems to work more consistently for quadruped setups). There's still one annoying bug regarding foot roll, but it's not blocking. I'll track it down later.
- Mouth rig now creates corrective shape keys on the face mesh for dealing with mouth corners when they spread open.
- Biped arm and leg types now cause mesh to scale when you scale the fk controls.
- Misc improvements to the rig types.