auto_now using signals
There has been some discussion about removing `auto_now` and `auto_now_add` some time ago. `auto_now_add` can be replaced be using a callable default value, `auto_now` can't. So I wrote this litte function for my current project (older ones still use `auto_add`) to fill the gap...but I'm not sure if `auto_now` will be removed at all.
- datetime
- model
- auto_now