Move headers under the hf directory.

This helps distinguish local headers from the more official headers.

Change-Id: I535c1b44081b9d60ba63666cd1ad514aaaf2c68d
diff --git a/src/api.c b/src/api.c
index f6895ca..4176941 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1,7 +1,8 @@
-#include "api.h"
+#include "hf/api.h"
 
-#include "std.h"
-#include "vm.h"
+#include "hf/std.h"
+#include "hf/vm.h"
+
 #include "vmapi/hf/call.h"
 
 struct vm secondary_vm[MAX_VMS];