Async support for Unity Twitter API tools

Recently I opened up these tools to make sure everything still worked as intended and realised that actually, none of what I had built could be performed naturally asynchronously! Sure you could wrap the example function calls inside a coroutine, but that didn't seem entirely suitable. 

In my day job I've been working with more recent C# features previously unavailable in Unity such as Asynchronous methods using the async and await keywords as well as writing code which is more orderly than post university me would have ever thought necessary. Disgusted at my old code, I decided it was time for an update.

New new set of tools feature essentially the same feature set of what was previously available but now have the added benefit of performance and readability improvements. Data structures have been moved to their own namespace, as have helper methods for getting an API access token.