more cleanup and documentation

lib/cable_holder.scad

@@ -1,6 +1,25 @@
 /*
+    This file is part of SBC Case Builder https://github.com/hominoids/SBC_Case_Builder
+    Copyright 2022,2023,2024 Edward A. Kisiel hominoid@cablemi.com
 
-    cableholder_spacer()
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>
+    Code released under GPLv3: http://www.gnu.org/licenses/gpl.html
+
+           NAME: cableholder_spacer
+    DESCRIPTION: creates 18650 and 21700 batteries
+           TODO: none
+
+          USAGE: cableholder_spacer()
 
 */