Add support for inverse diode direction

[chatelao]

IS

• Only row pins are driven
• Diodes in "Col -> Row" direction are not supported

SHOULD

• Inverse diode direction should be supported, e.g. with a flag on construction
• Then the column pins should then be be driven

I <3 Adafruit and will turn my head 90° until the fix arrives :-)

[dhalbert]

Another alternative is to use the built-in keypad module, https://learn.adafruit.com/key-pad-matrix-scanning-in-circuitpython/keymatrix, which supports diodes in both directions.