https://issues.apache.org/jira/browse/SPARK-12035

When we debuging lots of example code files, like in https://github.com/apache/spark/pull/10002, it's hard to know which file causes errors due to limited information in `include_example.rb`. With their filenames, we can locate bugs easily.

Author: Xusen Yin <yinxusen@gmail.com>

Closes #10026 from yinxusen/SPARK-12035.

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #9960 from yu-iskw/minor-remove-spaces.

https://issues.apache.org/jira/browse/SPARK-11336

mengxr I add a hyperlink of Spark on Github and a hint of their existences in Spark code repo in each code example. I remove the config key for changing the example code dir, since we assume all examples  should be in spark/examples.

The hyperlink, though we cannot use it now, since the Spark v1.6.0 has not been released yet, can be used after the release. So it is not a problem.

I add some screen shots, so you can get an instant feeling.

<img width="949" alt="screen shot 2015-10-27 at 10 47 18 pm" src="https://cloud.githubusercontent.com/assets/2637239/10780634/bd20e072-7cfc-11e5-8960-def4fc62a8ea.png">

<img width="1144" alt="screen shot 2015-10-27 at 10 47 31 pm" src="https://cloud.githubusercontent.com/assets/2637239/10780636/c3f6e180-7cfc-11e5-80b2-233589f4a9a3.png">

Author: Xusen Yin <yinxusen@gmail.com>

Closes #9320 from yinxusen/SPARK-11336.

The trim_codeblock(lines) function in include_example.rb removes some blank lines in the code.

Author: Xusen Yin <yinxusen@gmail.com>

Closes #9400 from yinxusen/SPARK-11443.

A POC code for making example code in user guide testable.

mengxr We still need to talk about the labels in code.

Author: Xusen Yin <yinxusen@gmail.com>

Closes #9109 from yinxusen/SPARK-10382.