[atari7800] Paddles and trackballs

I've done a two more proof of concept programs.  First, a version of the
paddle proof of concept which uses a DLI instead of a pseudo kernal. This
increases the amount of CPU time available to the rest of the program at the
cost of the number of paddle positions (0-31 for NTSC).

Second, a trackball proof of concept. I don't have one myself so I can't
test it out. Again, a DLI is used to sample the trackball multiple times per
screen.

I'm also planning on doing one for the driving controller.  I just have to
figure out Thomas's code from StellaList and make it work for both players.

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