Adding and removing items from the index

Does this client support basic operations like adding and removing items from an index? If I can't add to the index, there's little point me searching :-)

For example, using the [other package](https://github.com/knoxpo/dart_algolia) I can do something like:


Future addOrReplaceDeck(Deck deck) async {
AlgoliaIndexReference idx = algolia.instance.index('my_index');
var task = await idx.addObject(toJSON(deck));
}


Thank you!

Start at the Dart client's index API and compare the linked other package's addObject example. Trace how an index reference currently exposes operations, then determine the corresponding add/replace and remove behavior. Done means both basic operations are available through the client and verified against Algolia.

Written by the indexing model from the issue text.