VSCP MAX6675 thermocouple C i/f demo code for Raspberry Pi

This is work based on work done by Matthew Robinson (https://github.com/mttrb)

Enable spi interface with raspi-config before building. Also define version to build in the Makefile before building as of below

WIRINGPI - using the wiringpi library
PIGPIO - using the pigpio library (must be root)
PIGPIOIF2 - using the pigpio library and the pigpiod daemon (user space available)

pigpio

The pigpio library is described here

On Debian systems install with

sudo apt install pigpio pigpiod

The pigpiod daemon must be running to run this codde. To have it started on boot

sudo systemctl enable pigpiod

Manually start service with

sudo systemctl start pigpiod

and stop with

sudo systemctl start pigpiod