CHORE: Renaming API header folder

src/main.c

@@ -1,5 +1,5 @@
+#include <libstr/string.h>
 #include <stdio.h>
-#include <string/string.h>
 
 int
 main()

src/string.c

@@ -1,7 +1,7 @@
+#include <libstr/string.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <string/string.h>
 
 struct String
 {