Miscellaneous issues with file formats

[eliascarv]

1 - GeoJSON.jl writes table columns in arbitrary order;
2 - Shapefile.jl saves Chains and Polygons as Multi;
3 - The default number type in GeoJSON.jl is Float32, set this option with numbertype kwarg;
4 - GeoJSON.jl writes Date columns as string because the JSON format has no date types;
5 - KML file is failing to save with Shapefile.jl;