Updating I2C position encoders to enable babystepping and Babystep XY when using the ecm microstep correction method. Also changed default method to ECM microstep.
Reverse engineered from the unpublished firmware from Creality,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.
