Summary: Constrain format of classname and document Define the format of a valid classname. Updated design doc, function doc and glossary to document format. Error message for case where we have a redefinition of a classname now says why ValueError is raised since we are raising ValueError for incorrect classname format as well. Tests for all cases including verification of cause for ValueError exceptions.

--- a/doc/glossary.txt	Tue Jul 28 05:51:00 2020 -0400
+++ b/doc/glossary.txt	Tue Jul 28 06:24:39 2020 -0400
@@ -5,6 +5,9 @@
 
 class
    a definition of the properties and behaviour of a set of items
+classname
+   the name of a class. It must start with a letter, end with a letter
+   or "_", and only have alphanumerics and "_" in the middle.
 db (or hyperdb)
    a collection of items
 designator