bed_tilt: Add support for automatic bed tilt move transformation

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

config/example-extras.cfg

@@ -17,6 +17,41 @@
 #   command. The default is 0.
 
 
+# Bed tilt compensation. One may define a [bed_tilt] config section to
+# enable move transformations that account for a tilted bed.
+#[bed_tilt]
+#x_adjust: 0
+#   The amount to add to each move's Z height for each mm on the X
+#   axis. The default is 0.
+#y_adjust: 0
+#   The amount to add to each move's Z height for each mm on the Y
+#   axis. The default is 0.
+# The remaining parameters control a BED_TILT_CALIBRATE extended
+# g-code command that may be used to calibrate appropriate x and y
+# adjustment parameters.
+#points:
+#    A newline separated list of X,Y points that should be probed
+#    during a BED_TILT_CALIBRATE command. 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.
+#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.
+#probe_z_offset: 0
+#   The Z height (in mm) of the head when the probe triggers. The
+#   default is 0.
+#manual_probe:
+#   If true, then BED_TILT_CALIBRATE will perform manual probing. If
+#   false, then a PROBE command will be run at each probe
+#   point. Manual probing is accomplished by manually jogging the Z
+#   position of the print head at each probe point and then issuing a
+#   NEXT extended g-code command to record the position at that
+#   point. The default is false if a [probe] config section is present
+#   and true otherwise.
+
+
 # In a multi-extruder printer add an additional extruder section for
 # each additional extruder. The additional extruder sections should be
 # named "extruder1", "extruder2", "extruder3", and so on. See the