[SPARK-16266][SQL][STREAING] Moved DataStreamReader/Writer from pyspark.sql to pyspark.sql.streaming

## What changes were proposed in this pull request?

- Moved DataStreamReader/Writer from pyspark.sql to pyspark.sql.streaming to make them consistent with scala packaging
- Exposed the necessary classes in sql.streaming package so that they appear in the docs
- Added pyspark.sql.streaming module to the docs

## How was this patch tested?
- updated unit tests.
- generated docs for testing visibility of pyspark.sql.streaming classes.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #13955 from tdas/SPARK-16266.

1 files changed, 2 insertions, 1 deletions

diff --git a/python/pyspark/sql/context.py b/python/pyspark/sql/context.py
index b5dde13ed7..3503fb90c3 100644
--- a/python/pyspark/sql/context.py
+++ b/python/pyspark/sql/context.py
@@ -26,7 +26,8 @@ from pyspark import since
 from pyspark.rdd import ignore_unicode_prefix
 from pyspark.sql.session import _monkey_patch_RDD, SparkSession
 from pyspark.sql.dataframe import DataFrame
-from pyspark.sql.readwriter import DataFrameReader, DataStreamReader
+from pyspark.sql.readwriter import DataFrameReader
+from pyspark.sql.streaming import DataStreamReader
 from pyspark.sql.types import Row, StringType
 from pyspark.sql.utils import install_exception_handler