Now that the callback-based MongoClient has moved to the mongodb-driver-core module, even though it's internal (and won't appear in Javadoc) it's still public, which means that it will appear in IDE code completion. Since the class and interface names are all the same as the sync driver, it will be confusing to users of the sync driver to have them appear.

Let's prefix all the names with "Async", e.g. AsyncMongoClient, to avoid this confusion.