- solidify/face.h (struct face), solidify/face.c (read_face),
solidify/level.c (draw_map, draw_image): introduce inclination of the z0
plane
- solidify/level.c (draw_map): make blue z == z0 display more continuous
- solidify/level.c (scroll_event): moved z0 shift to scroll_z
- solidify/level.c (scroll_event, scroll_xy): added manipulation of the
z0 plane's inclination