Draw bone axes

Parse bone names and rest transforms from IQM
Refactor mesh loading to use temporary structs for modular modifications
Add conversion of float verts to vert8 / vert16
Add Matrix3x4_scale_rotate_translate util
Add mesh submesh splitting algorithm
Add float to u/int8/16 conversion helpers
Add bone set operations helpers
Add bone members to skeletal_model_t
Update skeletal_mesh_t recursive struct
Add IQM vert8 and vert16 structs