new json list of traces

public/datavelo/velotraces.json.php

@@ -0,0 +1,30 @@
+<?php
+$velotracks = "json";
+
+// An array of the json file names
+$tracks = array();
+
+//Open images directory
+$dir = opendir($velotracks);
+
+//List files in tracks directory
+while (($file = readdir($dir)) !== false) {
+  $geojson = json_decode(file_get_contents(__DIR__."/".$velotracks."/".$file));
+
+  if (isset($geojson->slug)) {
+    $date = $geojson->date;
+    $title = $geojson->title;
+    $slug = $geojson->slug;
+    $countries = $geojson->countries;
+    array_push($tracks,[
+	'date' => $geojson->date,
+	'title' => $geojson->title,
+	'slug' => $geojson->slug,
+	'countries' => $geojson->countries,
+    ]);
+  }
+}
+closedir($dir);
+// asort($tracks);
+echo json_encode($tracks);
+?>