Convert file descriptors to generic streams

src/lib/util.h

@@ -1,3 +1,11 @@
 #pragma once
 
+#include <stdint.h>
+
 #define NUL 0 // TODO Fix VSCode thinking `NULL` conflicts with some other definition.
+
+typedef uint64_t exit_code_t;
+
+#define EXIT_CODE_OK 0
+#define EXIT_CODE_NOT_FOUND ((uint64_t)-2)
+#define EXIT_CODE_GENERAL_FAILURE ((uint64_t)-1)