bed_screws: Add a helper tool for leveling bed screws

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

config/example-extras.cfg

@@ -107,8 +107,8 @@
 #   is above the bed at the given nozzle coordinates. The default is
 #   to not enable the command.
 #speed: 50
-#   The speed (in mm/s) of non-probing moves during the
-#   calibration. The default is 50.
+#   The speed (in mm/s) of non-probing moves during the calibration.
+#   The default is 50.
 #horizontal_move_z: 5
 #   The height (in mm) that the head should be commanded to move to
 #   just prior to starting a probe operation. The default is 5.
@@ -226,6 +226,43 @@
 #   results in more curvature in the mesh. Default is .2.
 
 
+# Tool to help adjust bed leveling screws. One may define a
+# [bed_screws] config section to enable a BED_SCREWS_ADJUST g-code
+# command.
+#[bed_screws]
+#screw1: 100,100
+#   The X,Y coordinate of the first bed leveling screw. This is a
+#   position to command the nozzle to that is directly above the bed
+#   screw (or as close as possible while still being above the bed).
+#   This parameter must be provided.
+#screw1_name: front screw
+#   An arbitrary name for the given screw. This name is displayed when
+#   the helper script runs. The default is to use a name based upon
+#   the screw XY location.
+#screw1_fine_adjust:
+#   An X,Y coordinate to command the nozzle to so that one can fine
+#   tune the bed leveling screw. The default is to not perform fine
+#   adjustments on the bed screw.
+#screw2:
+#screw2_name:
+#screw2_fine_adjust:
+#...
+#   Additional bed leveling screws. At least three screws must be
+#   defined.
+#horizontal_move_z: 5
+#   The height (in mm) that the head should be commanded to move to
+#   when moving from one screw location to the next. The default is 5.
+#probe_height: 0
+#   The height of the probe (in mm) after adjusting for the thermal
+#   expansion of bed and nozzle. The default is zero.
+#speed: 50
+#   The speed (in mm/s) of non-probing moves during the calibration.
+#   The default is 50.
+#probe_speed: 5
+#   The speed (in mm/s) when moving from a horizontal_move_z position
+#   to a probe_height position. The default is 5.
+
+
 # Multiple Z stepper tilt adjustment. This feature enables independent
 # adjustment of multiple z steppers (see stepper_z1 section below) to
 # adjust for tilt. If this section is present then a Z_TILT_ADJUST