Convert to platform.io build

[kallisti5]

We should investigate if platform.io can be used to build these BusPirate firmwares. Platform.io has "target board support" meaning we can simplify the code to build "all the firmwares at once". It will also handle pulling down toolchains, etc.

https://platformio.org/

[kallisti5]

• https://docs.platformio.org/en/latest/platforms/microchippic32.html (We use PIC16 (aka PIC24 though))

See platformio/platformio-core#704

[mikebdp2]

@kallisti5 It's not clear if they have Evaluation/Pro that's required to use optimization levels beyond 0. Without it, you can do the automatic builds only for BPv4 since BPv3 doesn't fit on level 0 (personally I set up a VM so that it has a temporary MAC address different to my physical one, this proprietary IDE is registered to it and is isolated)