Document async options

[markwalkom]

We support async methods for all the sync ones, but we don't talk about this at all in the docs.

Can we get something adding so people are aware of it?

[Mpdreamz]

Our long term plan here is to generate all our ApiTests and CrudTests to docs under

https://www.elastic.co/guide/en/elasticsearch/client/net-api/2.x/index.html

in an API section e.g

https://github.com/elastic/elasticsearch-net/blob/master/src/Tests/Document/Single/Get/GetApiTests.cs

Would live under api/document/single/get.html

We will pick one of the 4 ways (sync/async and inititalizer/fluent) through consistent hashing to fully describe the endpoint and its body and response handling.

Right now we only generate (some of) our UsageTests and we still have to work out how to nest the current docs better before we inject more pages all under the same banner :) e.g there is no subdivision under Query DSL and Aggregations in the docs but we would like it to reflect our folder structure (which mimics the es core docs).

[Mpdreamz]

closing this in favor of new tracking issue: #2248