Added mappers 66 and 71 (SMB/Duck Hunt and Codemasters, respectively).
Also made background sprites actually render behind the background, and fixed sprite priorities for 8x16 sprites (They were reversed before).
If you´re having trouble with SMB3, make sure that you have the PRG1 version of the ROM. Even then, it still freezes on the title screen half the time when you press Start... if it does this, reload the ROM and try it again. Once you start the game successfully though it should be playable There´s just something the title screen does that throws timing off.