Reworked the core examples to exclude contributed examples.

examples/Ex016_Using_Construction_Geometry.py

@@ -0,0 +1,21 @@
+import cadquery as cq
+
+# Create a block with holes in each corner of a rectangle on that workplane.
+# 1.  Establishes a workplane that an object can be built on.
+# 1a. Uses the named plane orientation "front" 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 Z face of the box.
+# 4.  Creates a new workplane to build new geometry on.
+# 5.  Creates a for-construction rectangle that only exists to use for placing
+#     other geometry.
+# 6.  Selects the vertices of the for-construction rectangle.
+# 7.  Places holes at the center of each selected vertex.
+result = cq.Workplane("front").box(2, 2, 0.5)\
+                 .faces(">Z").workplane() \
+                 .rect(1.5, 1.5, forConstruction=True).vertices() \
+                 .hole(0.125)
+
+# Displays the result of this script
+show_object(result)