Make forward/reverse weight/offset calculated at query time,

rather than being cached in the StaticRTree.  This means we
can freely apply traffic data and not have stale values lying
around.  It reduces the size of the RTree on disk, at the expense
of some additional data in RAM.

include/util/static_rtree.hpp

@@ -59,6 +59,13 @@ class StaticRTree
         std::uint32_t children[BRANCHING_FACTOR];
     };
 
+    struct LeafNode
+    {
+        LeafNode() : object_count(0), objects() {}
+        uint32_t object_count;
+        std::array<EdgeDataT, LEAF_NODE_SIZE> objects;
+    };
+
   private:
     struct WrappedInputElement
     {
@@ -79,13 +86,6 @@ class StaticRTree
         }
     };
 
-    struct LeafNode
-    {
-        LeafNode() : object_count(0), objects() {}
-        std::uint32_t object_count;
-        std::array<EdgeDataT, LEAF_NODE_SIZE> objects;
-    };
-
     using QueryNodeType = mapbox::util::variant<TreeNode, EdgeDataT>;
     struct QueryCandidate
     {