Create v0.10 branch
DB/Postgresql DB: base class for all pg based databases
Rename 'match_where' to 'db_selects'
DB/Postgresql DB: Move code from compile_sql (and similar)
Merge remote-tracking branch 'origin/db-postgresql-as-base-class' into db-overpass

Conflicts:
	pgmapcss/compiler/compile_sql.py
DB/Overpass: resolve set statements
DB/Overpass: improve db functions

- fix union in queries
- build either linestrings or polygons
- bugfixes