CocoaPods support

Added a valid podspec.

Auto generated message below ;)

I’ve recently added [Snappy-Slider](https://github.com/CocoaPods/Specs/tree/master/Snappy-Slider) to the [CocoaPods](https://github.com/CocoaPods/CocoaPods) package manager repo.

CocoaPods is a tool for managing dependencies for OSX and iOS Xcode projects and provides a central repository for iOS/OSX libraries. This makes adding libraries to a project and updating them extremely easy and it will help users to resolve dependencies of the libraries they use.

However, Snappy-Slider doesn't have any version tags. I’ve added the current HEAD as version 0.0.1, but a version tag will make dependency resolution much easier.

[Semantic version](http://semver.org) tags (instead of plain commit hashes/revisions) allow for [resolution of cross-dependencies](https://github.com/CocoaPods/Specs/wiki/Cross-dependencies-resolution-example).

In case you didn’t know this yet; you can tag the current HEAD as, for instance, version 1.0.0, like so:

```
$ git tag -a 1.0.0 -m "Tag release 1.0.0"
$ git push --tags
```