Fix Linux build issues and bugs
MS3D loading (partial patch)
ms3d: Fix some structs, finish ms3d_meta()
ms3d: Tweak structs and work on ms3d_data()

Still need to load and process triangle data.
mesh/ms3d.c: Add comments to private functions
engine/mesh: Add mesh flags
Add ms3d engine test
Fix post-rebase issues
engine/mesh: Add load_ms3d()

General mesh loading procedure for MS3D files
Add free_mesh_data() macro, remove mesh_data.c
test/engine/ms3d: Add dwarf mesh load/clear