Move headers under the hf directory.

This helps distinguish local headers from the more official headers.

Change-Id: I535c1b44081b9d60ba63666cd1ad514aaaf2c68d
diff --git a/src/cpio.c b/src/cpio.c
index c6db268..d613e54 100644
--- a/src/cpio.c
+++ b/src/cpio.c
@@ -1,8 +1,8 @@
-#include "cpio.h"
+#include "hf/cpio.h"
 
 #include <stdint.h>
 
-#include "std.h"
+#include "hf/std.h"
 
 #pragma pack(push, 1)
 struct cpio_header {