Improve documentation of fl_strdup()

and add example of value of fl_mac_os_version.

FL/fl_string_functions.h

@@ -16,20 +16,20 @@
 
 /**
   \file fl_string_functions.h
-  \brief Public header for FLTK's own platform agnostic string handling.
+  Public header for FLTK's platform-agnostic string handling.
 */
 
 #ifndef _FL_fl_string_functions_h_
 #define _FL_fl_string_functions_h_
 
 #include "Fl_Export.H"
-#include "fl_types.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-/** \addtogroup fl_string
+/** \defgroup fl_string  String handling functions
+ String handling functions declared in <FL/fl_string_functions.h>
     @{
 */
 
@@ -37,8 +37,6 @@ FL_EXPORT char* fl_strdup(const char *s);
 
 /** @} */
 
-/*****************************************************************************/
-
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */

FL/mac.H

@@ -161,7 +161,7 @@ extern FLWindow *fl_mac_xid(const Fl_Window *win);
 extern Fl_Window *fl_mac_find(FLWindow *);
 class Fl_Gl_Window;
 
-/** The version number of the running Mac OS X (e.g., 100604 for 10.6.4, 101300 for 10.13).
+/** The version number of the running Mac OS X (e.g., 100604 for 10.6.4, 101300 for 10.13, 140102 for 14.1.2).
  FLTK initializes this global variable before main() begins running. If
  the value is needed in a static initializer, a previous call to Fl::system_driver()
  makes sure \ref fl_mac_os_version has been initialized.