Officially support "ndjson"

[hgschmie]

While it is possible to massage the object mapper enough to produce newline-delimited json ("ndjson", see http://ndjson.org/), it would be great to have "official" support in Jackson through a module. Reading ndjson into a collection, list or stream would be straightforward as well (e.g. see https://github.com/CjHare/systematic-trading/blob/master/systematic-trading-backtest-output-elastic/src/main/java/com/systematic/trading/backtest/output/elastic/serialize/NdjsonListSerializer.java for a basic example on what a serializer could look like).