snes: work on enemies some more

in theory now we are selecting one of 8 types
snes: attempt to fix issue when top of B/A is not zero

Still not working
snes: validate all rep/sep setting register size

URGH I hate how they did this, and it would be nicer if it
had a better mnemonic.  I guess I could redefine myself.

anyway all of them should be proper now
snes: make activate sprite 16-bit accumulator clean

now things are working again
snes: finish commenting svmwgraph code