Moved all the mechanical stuff into a subdirectory

mechanical/lib.scad

@@ -0,0 +1,14 @@
+module bom_item(printable = true, label = "") {
+  print_label = printable ? " print " : " stock ";
+  item_label = label == "" ? parent_module(1) : label;
+  echo(str("BOM:", print_label, item_label));
+}
+
+module slotify(vector) {
+  for (child = [0:$children-1]) {
+    hull() {
+      children(child);
+      translate(vector) children(child);
+    }
+  }
+}