pack(): introduced a new helper for packing parts into a 2D footprint.

Also added documentation for the new facility as well as a nascent
CONTRIBUTING.md to collect pointers to the tools used by developers of
this project.

examples/packed_boxes.py

@@ -0,0 +1,34 @@
+"""
+
+name: packed_boxes.py
+by:   fischman
+date: November 9th 2023
+
+desc: Demo packing a bunch of boxes in 2D.
+
+"""
+import functools
+import operator
+import random
+import build123d as bd
+
+random.seed(123456)
+test_boxes = [bd.Box(random.randint(1, 20), random.randint(1, 20), random.randint(1, 5))
+              for _ in range(50)]
+packed = bd.pack(test_boxes, 3)
+
+# Lifted from https://build123d.readthedocs.io/en/latest/import_export.html#d-to-2d-projection
+def export_svg(parts, name):
+    part = functools.reduce(operator.add, parts, bd.Part())
+    view_port_origin=(0, 0, 150)
+    visible, hidden = part.project_to_viewport(view_port_origin)
+    max_dimension = max(*bd.Compound(children=visible + hidden).bounding_box().size)
+    exporter = bd.ExportSVG(scale=100 / max_dimension)
+    exporter.add_layer("Visible")
+    exporter.add_layer("Hidden", line_color=(99, 99, 99), line_type=bd.LineType.ISO_DOT)
+    exporter.add_shape(visible, layer="Visible")
+    exporter.add_shape(hidden, layer="Hidden")
+    exporter.write(f"../docs/assets/{name}.svg")
+
+export_svg(test_boxes, "packed_boxes_input")
+export_svg(packed, "packed_boxes_output")