added documentation for new option in 'refresh/remove_before'. get modification time from file
added documentation for new option in 'refresh/remove_before'. get modification time from file

olt/mapproxy,procrastinatio/mapproxy,mapproxy/mapproxy,Anderson0026/mapproxy,faegi/mapproxy,olt/mapproxy,kaiCu/mapproxy,Anderson0026/mapproxy,kaiCu/mapproxy,drnextgis/mapproxy,geoadmin/mapproxy,camptocamp/mapproxy,mapproxy/mapproxy,vrsource/mapproxy,camptocamp/mapproxy,drnextgis/mapproxy,vrsource/mapproxy,faegi/mapproxy,procrastinatio/mapproxy,geoadmin/mapproxy