Rename the template_for header.

C++26 (I hope) is supposed to have this syntax:

```
template for( const auto &element: aggregate )
{
	...;
}
```

Thus, I've adjusted this gadget to have a similar name, to enable
simple mechanical code changes.  From Alepha, you'd use it
thus:

```
template_for( aggregate ) <=[&]( const auto &element )
{
	...;
};
```

CMakeLists.txt

@@ -38,7 +38,7 @@ add_subdirectory( comparisons.test )
 add_subdirectory( Exception.test )
 add_subdirectory( word_wrap.test )
 add_subdirectory( string_algorithms.test )
-add_subdirectory( template_for_each.test )
+add_subdirectory( template_for.test )
 add_subdirectory( tuplize_args.test )
 add_subdirectory( Thread.test )
 add_subdirectory( assertion.test )