Long Hikes: every track, as GPX

For each trail or route whose record includes a track:

  <id>/<id>.gpx              the main track, simplified to 5 m
  <id>/<id>-alternates.gpx   alternate and connector tracks, simplified to 5 m, where the
                             source serves them separately
  <id>/release.txt           the source, licence and date the track files came from

and at the top:

  trails.csv    one row per record, with its licence
  SOURCES.md    each source, its terms, and the trails that use it

Terms. Each track keeps its source's terms and needs its source's credit, as
given in its <id>/release.txt (the Licence and Attribution lines) and in
trails.csv (the licence column). Tracks from OpenStreetMap are
© OpenStreetMap contributors, under the ODbL. The records themselves are
public domain (CC0-1.0).

The GPX files are simplified to 5 m, with coordinates to 6 decimal places.
The full-resolution tracks are in all-geojson.zip.
