patch: disputed boundaries

[yetzt]

fixed version of #5 as proposed in shortbread-docs/#1

[Nakaner]

I pushed a commit onto your branch to make the things work as expected.

I build vector tiles for the boundary-lines layer of the Geofabrik Asia OSM extract. Blue lines have disputed=true, green lines disputed=false in the vector tiles.

The western half of Crimea is missing because it is outside the Asia clipping polygon. Boundary lines of the Kashmir and Ladakh region are missing because type=boundary was set on the boundary was (I removed the tags from OSM today).

I will investigate whether ignoring relations with boundary=disputed and admin_level>4 will improve the result. Many of the relations with boundary=disputed do not have admin_level=*, they will not be ignored.

[yetzt]

ah, good point, i was only really interested in looking at admin_level=2.

[Nakaner]

If boundary=disputed with admin_level=2/3/4 or missing admin_level are accepted only, some boundary lines around West bank loose their disputed=true.