New protocol decoder: Microchip MRF24J40

We're happy to announce that libsigrokdecode supports yet another new protocol decoder: mrf24j40.

This PD decodes the SPI-based protocol of the Microchip MRF24J40, an IEEE 802.15.4 2.4 GHz RF tranceiver chip.

As usual we also have a few sample dumps in the sigrok-dumps repository, and a few test-cases in sigrok-test.

The decoder was contributed by Karl Palsson, thanks a lot!