Feature request: Implement hardware-based "safe mode" limits via hardware pin

[rjmcdougall]

We find an frequent need to limit our board's max speed when gifting rides to less experienced riders. In an implementation prior to VESC we implemented a "speed-pin" -- a removable dongle to neuter the board into a safer mode. This was a simple two-pin switch activated by presence of the "speed-pin".

Would it be possible implement a feature to limit eRPM based on an external hardware switch?

(the hardware device is preferred over the app-modes for ease of use).

If it's helpful, I could suggest an implementation via a pull request?

[AkbarRamzan]

This should be very easy to do with a lisp script. Perhaps someone could create an example