NDJSON and similar

[jacobwilliams]

Other possible flavors to support:

• NDJSON https://github.com/ndjson/ndjson-spec
• JSON Text Sequences https://tools.ietf.org/html/rfc7464
• JSON Lines http://jsonlines.org

Note: I think we can currently write these fine (just use a loop and add the new lines, etc. yourself). But we can't parse a file like this.

Maybe worth adding support.

[jacobwilliams]

Note: see also #328

[mk-pmb]

See also https://en.wikipedia.org/wiki/JSON_streaming , I especially like record-separated JSON. Maybe I can soon make a PR.