Requests an asynchronous close of the stream, releasing resources related to it.
When the operation is finished
callback will be called. You can then call close_async.end to
get the result of the operation.
For behaviour details see close.
The asynchronous methods have a default fallback that uses threads to implement asynchronicity, so they are optional for inheriting classes. However, if you override one you must override all.
the io priority of the request
optional cancellable object
callback to call when the request is satisfied
the data to pass to callback function