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, 2 insertions, 1 deletions

diff --git a/array.c b/array.c
index f5a34cf..b1e55b2 100644
--- a/array.c
+++ b/array.c
@@ -2,9 +2,10 @@
 #include <string.h>
 #include <errno.h>
 
-#include "array.h"
 #include "util.h"
 
+#include "array.h"
+
 #define ARRAY_SIZE 16
 
 void array_init(Array *arr) {