Reverse engineered from the unpublished firmware from Creality,
inferring the base version and configuration they used. The basis is
the firmware version from "Jul 31 2017 10:16:30". Configurations were
found by seeing what code was compiled into the firmware, and
constants used there.
They used Marlin 1.0.1, because
* 1.0.0 had very different serial output in `setup()` and overall
code structure.
* 1.0.2 changed the `VERSION_STRING` to include a leading space,
and `lcd_init` uses `SET_INPUT` instead of `pinMode`.
For U8Glib, a version between 1.14 and 1.17 was used, because
* 1.12 didn't have the extra speed argument to u8g_InitCom.
* 1.13 didn't have the soft reset instruction for UC1701 initialization.
* 1.18 has a new directory structure.
Quirks
* The value of PID_dT hints that F_CPU is 20M, but MarlinSerial.begin
suggests it's indeed 16M (and the board uses 16M). Left at 16M for now.
* The LED and DOGLCD_CS are on the same pin.
