DB/Overpass: add option to set a different overpass api url
DB/Overpass: handle error message when areas are not available in overpass api
DB/Overpass: Bugfix, multipolygons: not all outer ways in bbox
Merge branch 'db-overpass' of github.com:plepe/pgmapcss into db-overpass
Compile DB selects: change list of conditions to list instead of set
DB/Overpass: first compile to tokens, then to strings; also compile other conditions
DB/Overpass: merge conditions if they build subsets
DB/Overpass: merge conditions if one of them queries for key
DB/Overpass: Bugfix simplifying conditions (check references)
DB/Overpass: combine conditions to regular expressions
DB/Overpass: compiling regexp: collect in set, compile in last step
DB/Overpass: fix escaping values to regexp