Move Pods.xcodeproj from xcworkspace to xcodeproj

Allow users to build and run example app using project (as well as workspace) avoiding following error:
![screen shot 2013-11-18 at 12 51 23 pm](https://f.cloud.github.com/assets/1630490/1561395/120df2e2-5030-11e3-8af6-7755e865f4b3.png)
Using only workspace is typical for developers who are familiar with CocoaPods but not typical for those who not.