Unable to Build Documentation
```bash

python make.py html

Traceback (most recent call last):
  File "doc/make.py", line 23, in <module>
    import pandas
ModuleNotFoundError: No module named 'pandas'
```

I believe a slight bug was introduced by c8859b57b891701f250fb05f2cc60d2e6cae2d6b in including `import pandas` at the top of the script. Unless the user has pandas installed as a package I don't think this module would know where to find it without modifying the path or being more explicit on import

@jorisvandenbossche 