Support for .poly files

[sheerun]

There are some databases of city bounds that use .poly files instead of geojson. Could you support it?

e.g. https://github.com/JamesChevalier/cities

[drewda]

@sheerun thanks for the suggestion. Yes, we'll consider this as a future addition.

In the meantime, if you'd like to convert POLY files to/from GeoJSON or another format, see: https://wiki.openstreetmap.org/wiki/Osmosis/Polygon_Filter_File_Format#Converting_to.2Ffrom_POLY_format