v5.1.1

See CHANGELOG for full details. Here's a quick summary:

• Many thanks to @mbloch for help with debugging Mapshaper <> PostGIS compatibility

GENERAL

1. Ensure "empty" text fields have minimum length of 1 char for PostGIS compatibility. As the housekeeping DBFs are joined with the Mapshaper cracked features, the 5.y.z series would produce zero length text fields, which are valid but are incompatible with PostGIS. A new version of Mapshaper, used here, now produces a minimum of 1 char text length fields even if all column values are empty. Fixes #674