OpenPicoRTOS v1.9.1

[jnaulet]

This version adds support for Renesas RA4 series in general & Arduino Uno R4 Minima in particular.
ADC, Clocks, GPIOs, Multiplexing, PWMs, SPIs & UARTs are supported in quite a minimalistic way.

TWI/I2C needs further testing (code is available in the staging tree).
Other peripherals are not supported yet.

On the minor side, the auto-generated config can now be included simply by including picoRTOS.h