JIRA [here](https://issues.apache.org/jira/browse/SPARK-7581).

CC jkbradley

Author: Xusen Yin <yinxusen@gmail.com>

Closes #6113 from yinxusen/SPARK-7581 and squashes the following commits:

1a7d80d [Xusen Yin] merge with master
892a8e9 [Xusen Yin] fix python 3 compatibility
ec935bf [Xusen Yin] small fix
3e9fa1d [Xusen Yin] delete note
69fcf85 [Xusen Yin] simplify and add python example
81d21dc [Xusen Yin] add programming guide for Polynomial Expansion
40babfb [Xusen Yin] add java test suite for PolynomialExpansion