How can I implement this [emacs auto time stamp](https://www.gnu.org/software/emacs/manual/html_node/emacs/Time-Stamps.html) in vim? 

I have the following string at the top of a file: 

```
// Time-stamp: <> 

```

Here `//` are comment characters. 

What do I need to do so that on saving the file, gvim auto updates that time stamp field to: 

```
// Time-stamp: <DATE TIME USER> 

```

On every subsequent save, the date, time, user must be updated.

It would be useful to have this implemented in vim so that both emacs and vim users can auto update the time stamp on saving files.