An alternative CopyFromSerial implementation

[faceless2]

I've had the same issue as #32 - CopyFromSerial.ino appeared to work but didn't upload anything. Debugging by LED flashes is a bad option and made more complicated by the fact this I'm working on a (very old) Teensy 3.2 where the LED pin was shared with SS.

So I want to offer an alternative for anyone else failing to make progress with this, which is https://github.com/faceless2/SerialFlash-manager - firrmware and command-line tool (in NodeJS) for uploading and downloading to SPI Flash, which sends feedback over the serial port so you can monitor progress.

Paul, I hope this is OK raising as an issue - it sort of is, given I couldn't get the supplied example working, but I also don't want to tread on your toes by pointing to a different repository. If you don't think this is appropriate as an issue then please go ahead and close this.