Reworked the core examples to exclude contributed examples.

examples/Ex021_Splitting_an_Object.py

@@ -0,0 +1,25 @@
+import cadquery as cq
+
+# Create a simple block with a hole through it that we can split.
+# 1.  Establishes a workplane that an object can be built on.
+# 1a. Uses the X and Y origins to define the workplane, meaning that the
+#     positive Z direction is "up", and the negative Z direction is "down".
+# 2.  Creates a plain box to base future geometry on with the box() function.
+# 3.  Selects the top-most face of the box and establishes a workplane on it
+#     that new geometry can be built on.
+# 4.  Draws a 2D circle on the new workplane and then uses it to cut a hole
+#     all the way through the box.
+c = cq.Workplane("XY").box(1, 1, 1).faces(">Z").workplane() \
+                      .circle(0.25).cutThruAll()
+
+# 5.  Selects the face furthest away from the origin in the +Y axis direction.
+# 6.  Creates an offset workplane that is set in the center of the object.
+# 6a. One possible improvement to this script would be to make the dimensions
+#     of the box variables, and then divide the Y-axis dimension by 2.0 and
+#     use that to create the offset workplane.
+# 7.  Uses the embedded workplane to split the object, keeping only the "top"
+#     portion.
+result = c.faces(">Y").workplane(-0.5).split(keepTop=True)
+
+# Displays the result of this script
+show_object(result)