* vec.h (class vec_prefix): Change into struct.
Rename field alloc_PRIVATE_ back to alloc_.
Rename field num_PRIVATE_ to num_.
Update all users.
(class vec<T, A, vl_embed>): Rename field pfx_PRIVATE_ to vecpfx_.
Rename field data_PRIVATE_ to vecdata_.
Update all users.
(class vec<T, A, vl_ptr>): Make every field public.
Rename field vec_PRIVATE_ back to vec_.
Update all users.