Initial basic static delta code drop

This has a very basic level of functionality (deltas can be generated,
and applied offline).  There is only some stubbed out pull code to
fetch them via HTTP.

But, better to commit this now and improve it from a known starting
point, rather than have it languish in a branch.

src/libostree/ostree-core-private.h

@@ -91,6 +91,16 @@ _ostree_get_relative_object_path (const char        *checksum,
                                   OstreeObjectType   type,
                                   gboolean           compressed);
 
+
+char *
+_ostree_get_relative_static_delta_path (const char        *from,
+                                        const char        *to);
+
+char *
+_ostree_get_relative_static_delta_part_path (const char        *from,
+                                             const char        *to,
+                                             guint              i);
+
 void
 _ostree_loose_path (char              *buf,
                     const char        *checksum,