v4.0.0

• Node 16 is now recommended.
• Docker has been updated to run on Debian 11. (#602, @acalcutt )
• Mapbox-Native has been replaced with MapLibre-Native to allow upgrades past node 10. (#602, @acalcutt )
• Templates have been changed to use maplibre-gl-js and leaflet. (#603, @acalcutt )
• All packages upgraded (#604 #610, @acalcutt )
• Add static renderer pool for static images to work around 'tile mode' changes in maplibre-native (#608, @acalcutt )