CRSFv3

An Arduino wrapper over the portable c_crsf core, which also runs on ESP-IDF and STM32. Frame layer with both header forms and both CRC polynomials, the full telemetry set, 0x16/0x17/0x18 channels, the parameter protocol in both directions, MAVLink and MSP tunnels with chunking and reassembly, 0x32 Direct Commands, multi-port routing and CRSFv3 baudrate negotiation. AVR needs the compile-time switches: define CRSF_ARDUINO_MINIMAL in src/crsf_local_conf.h and a receiver or transmitter station fits an ATmega328P with room to spare, at the cost of the tunnels and the parameter protocol. Compiles for five architectures and passes the host test suites.