APIs for the train tracker at #cccamp23

See c3toc.de and github.com/stblassitude/c3toctrack for more information.

• tracks.json: information about the tracks, in custom format
• tracks.geojson: information about the tracks, in GeoJson format
• trains.json: information about the trains, in particular, their current position, custom format
• trains.geojson: information about the trains, in GeoJson format