Implemented Bne_un_s instruction

[jonathanpeppers]

This is very rudimentary branching, programs such as:

pal_all(PALETTE);
byte x = 10;
if (x == 10)
    oam_spr(x, 40, 0x10, 3, 0);
ppu_on_all();
while (true) ;

This works if I change to:

byte x = 40;
if (x == 40)
    oam_spr(x, 40, 0x10, 3, 0);