[SPARK-3952] [Streaming] [PySpark] add Python examples in Streaming Programming Guide

Having Python examples in Streaming Programming Guide.

Also add RecoverableNetworkWordCount example.
As long as you're editing this file, it would be nice to fix the incorrect formatting of the list here; the current markdown renders as 

![image](https://cloud.githubusercontent.com/assets/50748/4673751/260a0d02-55a8-11e4-8ad1-6313cab2d4cc.png)