Move more of the utility headers into /include/mcaselector-lite.

These headers have no associated C files, and are mainly used for
utility logic.
Having them in `/include` makes them more easily located, and more
globally used.

We are using "classic" header guards here over `#pragma once` for better
support. Since `#pragma once` is defined by the compiler, rather than
standard C.
Why isn't it used across the project? I have no idea.

src/io/conf.c

@@ -7,11 +7,11 @@
 
 #include <assert.h>
 #include <inttypes.h>
+#include <mcaselector-lite/atrb.h>
+#include <mcaselector-lite/types.h>
 #include <stdlib.h>
 #include <string.h>
 
-#include "../types.h"
-#include "../util/atrb.h"
 
 /* Matches s1 with s2, returns a pointer to s1 where the match stopped. */
 static const char *strmat(const char *s1, const char *s2) PURE NONNULL((1, 2));