open fun write(data: Buffer): AsyncFile
open fun write(buffer: Buffer, position: Long, handler: Handler<AsyncResult<Void>>): AsyncFile
Write a io.vertx.reactivex.core.buffer.Buffer to the file at position position in the file, asynchronously.
If position lies outside of the current size of the file, the file will be enlarged to encompass it.
When multiple writes are invoked on the same file there are no guarantees as to order in which those writes actually occur
The handler will be called when the write is complete, or if an error occurs.
position - the position in the file to write it at
handler - the handler to call when the write is complete
Return
a reference to this, so the API can be used fluently