Additional level shapes (256x64, 64x256, 128x128)

[NovaSquirrel]

Right now only 256x32 ("Horizontal") levels are supported and 32x256 is tracked in #60 - I would like to add these (in order of priority):

• 256x64 ("Tall Horizontal") - 32K
• 64x256 ("Wide Vertical") - 32K
• 128x128 ("Square") - 32K
  128x64 and 64x128 should be doable but I don't think I actually need them

levelload.s uses GetLevelColumnPtr which will need to jump to a pointer that can be changed for each shape.
I think I also need updates in scrolling.s, renderlevel.s and renderlevel2.s - try to solve it with global variables (replacing constants constants), and if that fails, then use indirect jumps. Level shapes that take up 32KB do not need renderlevel2.s versions because they can't support a second layer.
GetLevelPtrXY is already set up for this.

Actor list in the level data easily has space for 128 blocks of height if I want to use those bits for that.
But I need to figure out some sort of good solution for the foreground data - maybe a special 1-byte command that can move around vertically.