v2.5.3

• Support loading elevation tiles directly from zip or tgz files.
• Uses a JSON file to maintain an index of tiles to increase startup speed.
  The location of the index file must be writable, defaulting to
  .tile-index.json in the tiles folder. Can be configured using the
  datasetDirIndex setting in trip-server.yaml. See
  conf/trip-server-dist.yaml in the source tree.