## What changes were proposed in this pull request?

This groups GLM methods (spark.glm, summary, print, predict and write.ml) in the documentation. The example code was updated.

## How was this patch tested?

N/A

(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

![screen shot 2016-06-21 at 2 31 37 pm](https://cloud.githubusercontent.com/assets/15318264/16247077/f6eafc04-37bc-11e6-89a8-7898ff3e4078.png)
![screen shot 2016-06-21 at 2 31 45 pm](https://cloud.githubusercontent.com/assets/15318264/16247078/f6eb1c16-37bc-11e6-940a-2b595b10617c.png)

Author: Junyang Qian <junyangq@databricks.com>
Author: Junyang Qian <junyangq@Junyangs-MacBook-Pro.local>

Closes #13820 from junyangq/SPARK-16107.