backend: non-functional code-fiddling: format codablock.c (clang-format

+ manual); add SPDX to all files; prefix include guards with Z_;
  move vim comment to bottom; remove some trailing spaces

backend/output.h

@@ -1,7 +1,7 @@
-/*  output.h - Common routines for raster/vector
-
+/*  output.h - Common routines for raster/vector */
+/*
     libzint - the open source barcode library
-    Copyright (C) 2020 - 2021 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2020-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -28,7 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #ifndef Z_OUTPUT_H
 #define Z_OUTPUT_H
@@ -52,4 +52,5 @@ INTERNAL void out_upcean_split_text(int upceanflag, unsigned char text[],
 }
 #endif /* __cplusplus */
 
+/* vim: set ts=4 sw=4 et : */
 #endif /* Z_OUTPUT_H */