Macro make_vox_spec

macro_rules! make_vox_spec {
    (
        $body:ty,
        struct $Spec:ident { $( $(+)? $field:ident: $ty:ty = $asset_path:literal),* $(,)? },
        |$self_pat:pat, $spec_pat:pat_param| $bone_meshes:block $(,)?
    ) => { ... };
}