abstract fun copyRecursive(from: String, to: String, recursive: Boolean, handler: Handler<AsyncResult<Void>>): FileSystem
Copy a file from the path from to path to, asynchronously.
If recursive is true and from represents a directory, then the directory and its contents will be copied recursively to the destination to.
The copy will fail if the destination if the destination already exists.
handler - the handler that will be called on completion
Return
a reference to this, so the API can be used fluently