Connecting to Postgres per-request instead of once up-front in VecTiles.Provider
Moved database connection completely include VectTiles.server.Response.save()
Merge pull request #135 from migurski/vectiles-connection-fix

Vectiles connection fix—Travis build passes and it seems to work.
Bumped to 1.49.0 with addition of S3 RRS option and VecTiles connection tweak
Added IDs to vector tiles output based on original feature geometry
Added explicit feature identifier to vectiles queries in __id__ column
Renamed "geometry_hash" column to "__hash__"
Part-way through replacing __hash__ with __id__ in vectiles server, need to handle bbox replacement in subquery
Handling SRID and bbox in new query_columns() function
Moved query_columns() call in vectiles provider so results can be cached
Stopped casting all vectiles feature IDs to strings
Switched to using a context manager for vectiles Postgres connections
Stopped selecting extra geometry response in vectiles to throw it away
Changed bbox in vectiles query_columns() to whole-world 900913
Switched magic column name in vectiles from "geometry" to "__geometry__"
Bumped to 1.49.1 with update to magic column names in VecTiles Provider
Bumped to 1.49.2 with fix to SQL bug in VecTiles Provider for limiting column queries
Returning seemingly-valid empty TopoJSON responses for any request
Moved vectiles bbox string construction down to Response object
Actually encoding non-multi geometries in vectiles to seemingly-valid TopoJSON