fix indirect y resolving indirect access twice.
fix rol/ror/lsr with accumlator handled as immediate.
Merge pull request #7 from haramako/fix_rol_ror_lsr_with_acc

fix rol/ror/lsr with accumlator handled as immediate.
decode_arg explicitly returns nil for :acc mode
Merge pull request #8 from haramako/fix_indirect_y_access

fix indirect y resolving indirect access twice.