how to read/write CityJSONSeq could be improved based on fio cat/collect

[hugoledoux]

right right it's a bit hidden how to read (stdin instead of a file) and to write (export jsonl) and perhaps we could use the old fio terminology: fio cat and collect

https://sgillies.net/2014/10/05/unix-style-spatial-etl-with-fio-cat-collect-and-load.html

Not sure it's clearer for the end users... just an idea that I am listing here.