Initital support for alternative database types
DB: add support for osmosis pgsnapshop schema (not finished)
DB/osmosis: implement objects_member_of(), objects_members(), objects_near()
DB/Documentation: some initial thoughts about the two supported databases
DB/osmosis: check if object is area -> convert geometry to polygon
DB/Documentation: update link relations
CHANGELOG: update with osmosis support
Merge pull request #61 from plepe/osmosis-pgsnapshot

Support osmosis pgsnapshot schema as database backend