Remove restriction that a type generator generates a single type

[SVN r9237]

generic_programming.html

@@ -294,7 +294,7 @@ namespace std {
     <h2><a name="type_generator">Type Generators</a></h2>
 
     <p>A <i>type generator</i> is a template whose only purpose is to
-    synthesize a single new type based on its template argument(s)<a href=
+    synthesize a new type or types based on its template argument(s)<a href=
     "#1">[1]</a>. The generated type is usually expressed as a nested typedef
     named, appropriately <tt>type</tt>. A type generator is usually used to
     consolidate a complicated type expression into a simple one, as in