DEPR: Adding script to detect deprecated features by version (#6581)
- [ ] closes #xxxx
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

thanks! hmm

```
(pandas) bash-3.2$ ./list_future_warnings.sh 
./list_future_warnings.sh: line 31: realpath: command not found
usage: dirname path
usage: dirname path
^C
```

? Oh, didn't know realpath was not available on Mac, I thougt it was standard unix. Let me check how can avoid using it.