z_thermal_adjust: Add Z thermal adjuster module (#4157)

Use a frame-coupled temperature probe to compensate for thermal
expansion in real-time.

Signed-off by: Robert Pazdzior <robertp@norbital.com>

docs/Config_Reference.md

@@ -1205,6 +1205,45 @@ the nature of skew correction these lengths are set via gcode. See
 [skew_correction]
 ```
 
+### [z_thermal_adjust]
+
+Temperature-dependant toolhead Z position adjustment. Compensate for vertical
+toolhead movement caused by thermal expansion of the printer's frame in
+real-time using a temperature sensor (typically coupled to a vertical section
+of frame).
+
+See also: [extended g-code commands](G-Codes.md#z_thermal_adjust).
+
+```
+[z_thermal_adjust]
+#temp_coeff:
+#   The temperature coefficient of expansion, in mm/degC. For example, a
+#   temp_coeff of 0.01 mm/degC will move the Z axis downwards by 0.01 mm for
+#   every degree Celsius that the temperature sensor increases. Defaults to
+#   0.0 mm/degC, which applies no adjustment.
+#smooth_time:
+#   Smoothing window applied to the temperature sensor, in seconds. Can reduce
+#   motor noise from excessive small corrections in response to sensor noise.
+#   The default is 2.0 seconds.
+#z_adjust_off_above:
+#   Disables adjustments above this Z height [mm]. The last computed correction
+#   will remain applied until the toolhead moves below the specified Z height
+#   again. The default is 99999999.0 mm (always on).
+#max_z_adjustment:
+#   Maximum absolute adjustment that can be applied to the Z axis [mm]. The
+#   default is 99999999.0 mm (unlimited).
+#sensor_type:
+#sensor_pin:
+#min_temp:
+#max_temp:
+#   Temperature sensor configuration.
+#   See the "extruder" section for the definition of the above
+#   parameters.
+#gcode_id:
+#   See the "heater_generic" section for the definition of this
+#   parameter.
+```
+
 ## Customized homing
 
 ### [safe_z_home]