Move headers under the hf directory.

This helps distinguish local headers from the more official headers.

Change-Id: I535c1b44081b9d60ba63666cd1ad514aaaf2c68d
diff --git a/src/alloc.c b/src/alloc.c
index cd6844a..0e4f468 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1,7 +1,7 @@
-#include "alloc.h"
+#include "hf/alloc.h"
 
-#include "dlog.h"
-#include "spinlock.h"
+#include "hf/dlog.h"
+#include "hf/spinlock.h"
 
 static size_t alloc_base;
 static size_t alloc_limit;