Additional Framework support

[cujomalainey]

The following frameworks appear to be the best targets for porting the library going forward

Update as of march 2020, platformio supports zephyr

• [X] Arduino
  • [X] UART - done
  • [x] ~SPI~ - no slave support
  • [x] Softdevice
• [X] Mbed
  • [ ] SPI - blocked by SPI issues with my Teensy
  • [x] UART
  • [ ] SoftDevice (Native)
• [ ] ESP-IDF - branched and looks feasible
  • [ ] SPI
  • [ ] UART
• [ ] Simba
  • [ ] SPI
  • [ ] UART
• [ ] Zephyr - Zephyr is now on platformio (I am testing with a Argon board)
  • [ ] SPI
  • [ ] UART - Blocked by https://github.com/zephyrproject-rtos/zephyr/issues/24496
  • [ ] SoftDevice (Native)

Please leave comments here if there is another platform you think would be a good additional target. This work is planned for after the next release of antplus-arduino which releases the shifting and MOxy master profiles