Drivers for 4x4 Keypad spin and BS-2

So I was using the spin library driver with the 4x4 keypad and ran into this same problem. And it was for the same reason: Electrical Noise with nowhere to go goes nowhere.

I put 1K pulldowns on the column pins and wrote a new driver/demo. It very carefully drives only a single row at a time so that pressing multiple vertically aligned keys (say 1 and 4) does not cause a problem.

While I was at it, I wrote a little BS-2 program that uses pulldowns rather than the series resistors in the standard example.

The other thing I did was return, in addition to the raw bitmap, a count of the number of keys pressed and a coded value that is easier to use (0..9 for the numerics, 10..13 for A..D, etc)
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