[libng16] Mention prototype format in the documentation (libpng style guide)

libpng-manual.txt

@@ -1,6 +1,6 @@
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.6.10rc04 - March 4, 2014
+ libpng version 1.6.10rc04 - March 5, 2014
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2014 Glenn Randers-Pehrson
@@ -11,7 +11,7 @@ libpng-manual.txt - A description on how to use and modify libpng
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.6.10rc04 - March 4, 2014
+ libpng versions 0.97, January 1998, through 1.6.10rc04 - March 5, 2014
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2014 Glenn Randers-Pehrson
 
@@ -5337,8 +5337,8 @@ We don't use C++ style ("//") comments. We have, however,
 used them in the past in some now-abandoned MMX assembler
 code.
 
-Functions and their curly braces are not indented, and
-exported functions are marked with PNGAPI:
+Functions and their curly braces are not indented, exported
+functions are marked with PNGAPI:
 
  /* This is a public function that is visible to
   * application programmers. It does thus-and-so.
@@ -5349,6 +5349,9 @@ exported functions are marked with PNGAPI:
     body;
  }
 
+The return type and decorations are placed on a separate line
+ahead of the function name, as illustrated above.
+
 The prototypes for all exported functions appear in png.h,
 above the comment that says
 
@@ -5413,7 +5416,7 @@ Other rules can be inferred by inspecting the libpng source.
 
 XVI. Y2K Compliance in libpng
 
-March 4, 2014
+March 5, 2014
 
 Since the PNG Development group is an ad-hoc body, we can't make
 an official declaration.