Let geojson files in mapping be specified relative to mapping files

[pnorman]

Context

Right now when specifying a geojson file for geojson_intersects_feature it needs to be specified as an absolute path or relative to the imposm binary. This makes it difficult to distribute a mapping.yaml file with associated geojson in a way that doesn't depend on deployment-specific paths.

Expected Behavior

A relative path in a mapping file is relative to the mapping file.

Possible Fix

Change the current working directory before

imposm3/mapping/columns_intersection.go

Line 41 in 3b6e6b3

f, err := os.Open(geojsonFileName)