mark all functions in headers with VIS_EXPORT or VIS_INTERNAL

if vis actually wants to be a library exported symbols may need
mark up depending on the platform (eg. __declspec(dllexport)).
This needs to be hidden behind a macro because the way you export
is not the same on every platform.

I did this based on the assumption that vis.h was supposed to be
the only interface to the "vis" library. Since nobody actually
uses vis as a library I have no idea if this is actually correct.

Anyway marking up all prototypes like this allows for one to
convert all functions to static if a single translation unit is
used by inserting at the start:

 #define VIS_INTERNAL static
 #define VIS_EXPORT   static

1 files changed, 6 insertions, 1 deletions

diff --git a/util.h b/util.h
index d84846a..8b39c1e 100644
--- a/util.h
+++ b/util.h
@@ -1,8 +1,13 @@
 #ifndef UTIL_H
 #define UTIL_H
 
-#include <stdint.h>
+#ifndef VIS_INTERNAL
+  #define VIS_INTERNAL
+#endif
+
 #include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
 
 #define LENGTH(x)  ((int)(sizeof (x) / sizeof *(x)))
 #define MIN(a, b)  ((a) > (b) ? (b) : (a))