DOC: Clean up Sphinx Issues, fix tabs, in Cookbook

This is a follow on PR as a result of [seeing travis and sphinx render ~30 in line examples for the cookbook] (https://github.com/pydata/pandas/pull/8288#issuecomment-58734824).

Continues to address #6918

Initial PR: https://github.com/pydata/pandas/pull/8288

PS - apologies for wanting to rush the first PR.  My evening opened up unexpectedly.  Feel free to merge this latest, or provide more feedback for me to work on later. I'm going off grid for 2+ days after this.

The latest rendering is [here](https://cloud.githubusercontent.com/assets/6062071/4601203/f3dcdc76-50f0-11e4-8466-4db698bdc3b4.png):

![pandascookbook4](https://cloud.githubusercontent.com/assets/6062071/4601203/f3dcdc76-50f0-11e4-8466-4db698bdc3b4.png)