Add podspec

I’ve already pushed the podspec to the main CocoaPods/Specs repo, but it’s always nice to keep a copy of the file in the library repo itself.

BTW, you should start to add git tags to your repo. It will become necessary in order to push new versions of your code to CocoaPods.

``` bash
$ git tag '0.1.0'
$ git push --tags
```

Thanks for the project, it looks really good. :sunglasses: