Better document Extended Sprite Image Sets

[AwesomeDolphin]

Describe where we can find the problematic topic
Appendix Q: VIC-IV Video Interface Controller
Section: Sprites/Extended Sprite Image Sets

Describe the solution you'd like
The 16-bit sprite pointers still point to 64-byte blocks, so sprites need to be 64 bit aligned. This is implied by the documentation because it refers to the 16-bit word pointing to 4 GB of memory, but it never comes out and says it's still pointing to the old blocks, and even says it's an "absolute address".

However, the sprite pointers themselves need to be 16-byte aligned. This is not suggested by either the register bit layout, or the manual. I haven't quite worked out if the low 3 or 4 bits are just ignored, or if specifying an unaligned address upsets the VIC-IV, but the extended set only works if you say ".align 16"

Kibo figured it out immediately.

Describe alternatives you've considered
It could be that this should be fixed in the core.