Support of appending to already uploaded/stored files

I have looked in documentation and looking for appending to already existing files.
Microsoft Azure data lake store allows to [append data](https://docs.microsoft.com/en-us/azure/data-lake-store/data-lake-store-get-started-net-sdk#append-to-a-file) in already uploaded files.

Looking forward to this feature.
(PS. please close the issue if feature already exists and point me to it)