AUX GPIO Event Trigger ("Interrupts")

[Poofjunior]

The values configured as digital inputs need to be able to send Harp EVENT reply messages if their outputs rise, fall, or change.

We need to be able to configure which of the digital inputs will emit these messages, and on what condition they will emit. We can do this with 3 registers:

{
    uint8_t AuxGPIOInputEvent;
    uint8_t AuxGPIORise;
    uint8_t AuxGPIOFall;
}

The AuxGPIOInputEvent will configure which GPIOs will emit a message, and the following two registers will configure what pin change (or both) will emit the EVENT.

These events should emit from the AuxGPIOInputEvent or AuxGPIOState register.

[Poofjunior]

This is now implemented in #4 but the final registers ended up being:

    uint8_t AuxGPIOInputRiseEvent;
    uint8_t AuxGPIOInputFallEvent;
    uint8_t AuxGPIORisingInputs; // Raw state of which inputs rose (could be multiple)
    uint8_t AuxGPIOFallingInputs; // Raw state of which inputs fell (could be multiple