Use CocoaPods in example project

[pcantrell]

Switching the example project from Carthage to CocoaPods. Reasons:

• Despite its initial promise, Carthage adoption is low — and now looks like it will remain permanently low with SwiftPM coming. Far more users interesting in trying an example project will have CocoaPods installed.
• Carthage has proven inflexible, slow, difficult for new users to set up, and reluctant to adapt to user needs. CocoaPods is a terrifying behemoth, but one that works well.
• CocoaPods makes it easy to test Siesta changes locally in the example project, because it supports local file system dependencies. Carthage does not, and thus requires a push or hackery to test changes. (This shortcoming also forces a redundant checkout with Carthage.)
• This should make pod try work properly.

This is for the GithubBrowser example project only. The core Siesta project will continue to use Carthage for the time being.

Objections? Speak now!

[onekiloparsec]

I had so many nightmares with the Behemoth, as you say, I still prefer the simplicity and distributed philosophy of Carthage. But to give a try, CocoaPods has certainly a larger userbase.