screws_tilt_adjust: Add new screws_tilt_adjust tool (#1367)

Signed-off-by: Rui Caridade <rui.mcbc@gmail.com>

docs/G-Codes.md

@@ -274,6 +274,16 @@ section is enabled:
   the bed screws so that the bed is a constant distance from the
   nozzle.
 
+## Bed Screws Tilt adjust Helper
+
+The following commands are available when the "screws_tilt_adjust"
+config section is enabled:
+- `SCREWS_TILT_CALCULATE`: This command will invoke the bed screws
+  adjustment tool. It will command the nozzle to different locations
+  (as defined in the config file) probing the z height and calculate
+  the number of knob turns to adjust the bed level.
+  IMPORTANT: You MUST always do a G28 before using this command.
+
 ## Z Tilt
 
 The following commands are available when the "z_tilt" config section

docs/Manual_Level.md

@@ -133,3 +133,57 @@ prompt for coarse adjustments directly above each screw position, and
 once those are accepted, it will prompt for fine adjustments at the
 additional locations. Continue to use `ACCEPT` and `ADJUSTED` at each
 position.
+
+# Adjusting bed leveling screws using the bed probe
+
+This is another way to calibrate the bed level using the bed probe. To
+use it you must have a Z probe (BL Touch, Inductive sensor, etc).
+
+To enable this feature, one would determine the additional nozzle
+coordinates near the screws and add them to the config file. For example,
+it might look like:
+
+```
+[screws_tilt_adjust]
+screw1: -5,30
+screw1_name: front left screw
+screw2: 155,30
+screw2_name: front right screw
+screw3: 155,190
+screw3_name: rear right screw
+screw4: -5,190
+screw4_name: rear left screw
+horizontal_move_z: 10.
+speed: 50.
+samples: 3
+sample_retract_dist: 2.
+samples_result: median
+screw_thread: CW-M3
+```
+
+One can indicate the number of times to repeat probe on each screw and
+if the value is the median or the average read probe.
+
+The screw1 is always the reference point for the others, so the system
+assumes that screw1 is in the correct height.
+Then to use this feature you must preform every time `G28` before
+`SCREWS_TILT_CALCULATE` and after bed is probed you get an output like this:
+```
+Send: G28
+Recv: ok
+Send: SCREWS_TILT_CALCULATE
+Recv: // front left screw (Base): X -5.0, Y 30.0, Z 2.48750
+Recv: // front right screw : X 155.0, Y 30.0, Z 2.36000 : Adjust -> CW 01:15
+Recv: // rear right screw : X 155.0, Y 190.0, Z 2.71500 : Adjust -> CCW 00:50
+Recv: // read left screw : X -5.0, Y 190.0, Z 2.47250 : Adjust -> CW 00:02
+Recv: ok
+```
+This means that:
+
+    - front left screw is the reference point you must not change it.
+    - front right screw must be turned clockwise 1 full turn and a quarter turn
+    - rear right screw must be turned counter-clockwise 50 minutes
+    - read left screw must be turned clockwise 2 minutes (not need it's ok)
+
+Repeat the process several times until you get a good level bed, normally when
+all adjusts are below 6 minutes.