added prototype ZSTD_versionString()

lib/common/zstd_common.c

@@ -15,7 +15,7 @@
 #include <stdlib.h>         /* malloc */
 #include "error_private.h"
 #define ZSTD_STATIC_LINKING_ONLY
-#include "zstd.h"           /* declaration of ZSTD_isError, ZSTD_getErrorName, ZSTD_getErrorCode, ZSTD_getErrorString, ZSTD_versionNumber */
+#include "zstd.h"
 
 
 /*-****************************************
@@ -23,6 +23,8 @@
 ******************************************/
 unsigned ZSTD_versionNumber (void) { return ZSTD_VERSION_NUMBER; }
 
+const char* ZSTD_versionString(void) { return ZSTD_VERSION_STRING; }
+
 
 /*-****************************************
 *  ZSTD Error Management