Async Java SDK for Azure Cosmos DB

Now in preview, the new asynchronous Java SDK for the Azure Cosmos DB SQL API is now open sourced on GitHub. This SDK uses the popular RxJava library to add a new asynchronous API surface area for composing event-based programs with observable sequences. It also features an improved user experience, and is lighter weight than our previous synchronous Java SDK, yielding a significant performance improvement on the client-side. [Learn more.](https://azure.microsoft.com/en-us/blog/announcing-new-async-java-sdk-for-azure-cosmosdb) * Features