Adding podspec for TapkuLibrary 0.2.4

This adds the podspec for the newest version of [TapkuLibrary](https://github.com/devinross/tapkulibrary).

It's the newest version from the root of that repo, with a minor change to pass `pod lint` validation (adding a period at the end of the summary). I've submitted a [pull request](https://github.com/devinross/tapkulibrary/pull/239) to that project to update the podspec in that repo too.