vfp2csv does not handle multiple instances of vfp keywords

In `vfpfile2df` in `vfp2csv.py` you have the following lines:
```
print(f" - found {len(vfpstartindices)} vfp keywords")
for vfptableidx in vfpstartindices:
```
however the function returns `bhp_values_stacked` which is created inside the loop and so if `len(vfpstartindices) >1` you will still only get the result of the last vfp instance.

Is it common to have multiple tables in the same file? Can you have tables of different types within the same file? What is the intended behaviour? The tests do not really tell much as they all only have one instance of type VFPPROD..