Add support for json-lines in bulk loader

[dmsolow]

Json-lines (http://jsonlines.org/) is a commonly used format for storing a large number of JSON objects in a file. It's better than a single JSON array of objects because it makes it easy to read a file object by object without loading the entire thing into memory.

Popular big data processing frameworks like Apache Spark write JSON-lines natively (df.write.json("out.json") writes a JSON-lines file for each partition)

Support would probably be trivial to add for Dgraph and it would help people easily integrate Dgraph into existing ETL workflows.

[martinmr]

It doesn't seem like it would be too difficult to implement. We are gearing up for the 1.1 release so this issue most likely sit in the back-burner for a little while. If anybody else is interested in this feature, give a thumbs up to the issue so we can gauge interest and prioritize accordingly.