Author: cody koeninger <cody@koeninger.org>

Closes #6863 from koeninger/SPARK-8390 and squashes the following commits:

26a06bd [cody koeninger] Merge branch 'master' into SPARK-8390
3744492 [cody koeninger] [Streaming][Kafka][SPARK-8390] doc changes per TD, test to make sure approach shown in docs actually compiles + runs
b108c9d [cody koeninger] [Streaming][Kafka][SPARK-8390] further doc fixes, clean up spacing
bb4336b [cody koeninger] [Streaming][Kafka][SPARK-8390] fix docs related to HasOffsetRanges, cleanup
3f3c57a [cody koeninger] [Streaming][Kafka][SPARK-8389] Example of getting offset ranges out of the existing java direct stream api