add crossing_way validation

Tests are also added and passed.

One thing to note: I had to add the tree() function to history so that I can
use the tree in the test; hope that's fine.

data/core.yaml

@@ -638,6 +638,8 @@ en:
     many_deletions: "You're deleting {n} features: {p} nodes, {l} lines, {a} areas, {r} relations. Are you sure you want to do this? This will delete them from the map that everyone else sees on openstreetmap.org."
     tag_suggests_area: "The tag {tag} suggests line should be area, but it is not an area"
     deprecated_tags: "Deprecated tags: {tags}"
+    crossing_ways: Corssing ways without connection
+    crossing_ways_tooltip: "Roads are crossing other roads, buildings, railroads, or waterways without connection nodes or a bridge tag."
   zoom:
     in: Zoom in
     out: Zoom out