E-Ink adapter board and driver code

See https://hackaday.io/project/7443-e-ink-display-adapter.

Previous work and licensing

This is heavily based on previous work:

• PetteriAimonen explanations and PCB (unknown license) and driver code (public domain license)
• Sprite_tm explanations and PCB (CC-BY-SA license) and driver code (here's a github fork) (beer-ware license)
• zephray NekoCal project, in particular the driver code (MIT license)

Additionally, the driver code uses the esp-open-rtos ESP8266 SDK (various licenses).

As far as I'm concerned, I'd license this repository under the MIT license, but the PCB may be under CC-BY-SA, and there may be other restrictions if you use the esp-open-rtos SDK.