Environment variable for tile expiration min and max zoom

[balchen]

I have set up the tile server to run locally and it's working great with (almost) live updates as I update OSM. The only issue is that big tiles (low zoom levels) are not expired. Ideally, I would like to expire tiles to a lower zoom level than what is currently hard-coded in

openstreetmap-tile-server/openstreetmap-tiles-update-expire

Line 60 in 010f87d

EXPIRY_MINZOOM=13

.

If these values could be environment variables instead, I could configure the zoom level for tile expiration to suit different needs. I'll happily submit a PR for a change.

[nielsole]

probably docs should be updated, too.