[SPARK-10118] [SPARKR] [DOCS] Improve SparkR API docs for 1.5 release

cc: shivaram

## Summary

- Modify `tdname` of expression functions. i.e. `ascii`: `rdname functions` => `rdname ascii`
- Replace the dynamical function definitions to the static ones because of thir documentations.

## Generated PDF File
https://drive.google.com/file/d/0B9biIZIU47lLX2t6ZjRoRnBTSEU/view?usp=sharing

## JIRA
[[SPARK-10118] Improve SparkR API docs for 1.5 release - ASF JIRA](https://issues.apache.org/jira/browse/SPARK-10118)

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

Closes #8386 from yu-iskw/SPARK-10118.