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-varint.c

@@ -62,13 +62,15 @@ static const int max_varint_bytes = 10;
  * _ostree_read_varuint64:
  * @buf: (array length=buflen): Byte buffer
  * @buflen: Length of bytes in @buf
+ * @out_value: (out): Value
  * @bytes_read: (out): Number of bytes read
  *
- * Returns: An unsigned 64 bit integer value
+ * Returns: %TRUE on success, %FALSE on end of stream
  */
-guint64
+gboolean
 _ostree_read_varuint64 (const guint8   *buf,
                         gsize           buflen,
+                        guint64        *out_value,
                         gsize          *bytes_read)
 {
   guint64 result = 0;
@@ -92,8 +94,9 @@ _ostree_read_varuint64 (const guint8   *buf,
   } while (b & 0x80);
 
   *bytes_read = count;
+  *out_value = result;
 
-  return result;
+  return TRUE;
 }
 
 /**