`_save_struct_data` seems to be unused

[pmeier]

unlockNN/unlocknn/download.py

Line 154 in 128b192

def _save_struct_data(df: pd.DataFrame, fname: PathLike):

Grepping the repository reveals no usage. Given that it seems to be an internal functionality, maybe it can be removed?

[a-ws-m]

A good spot -- that function is used for serializing data so that it can be included in this repository and downloaded using unlocknn.download.load_data. At the time I thought it ought to be a private function because it would only really be used for adding more data to the repo (i.e. during development), but I realise that thinking was flawed. I'll make it a public function.

[pmeier]

Although 7c45497 made it public, it is not included in the documentation yet.

[a-ws-m]

It's now added here alongside instructions for adding one's own data.