CLI convert command

[eadmaster]

add a convert command in the cli interface to convert from one dataset format to another. e.g.:

$ fiona convert docs/data/test_uk.shp test_uk.json
$ fiona convert docs/data/test_uk.shp test_uk.gpx

[sgillies]

@eadmaster at the moment, conversion with Fiona is done by piping the output of fio cat to the input of fio load like this:

fio cat example.shp | fio load -f GPKG example.gpkg

It's relatively slow because of the serialization and deserialization between programs. But it's extendable via other filter-like programs like jq or https://fio-planet.readthedocs.io/en/latest/.

A general purpose conversion command, without serialization, would be useful but complicated. One look at the options of https://gdal.org/programs/ogr2ogr.html shows how complicated such a command can get when all of the filters and transforms must be built-in.