Validphys script to download hepdata tables
Created by: Radonirinaunimi
As far as I understood from the report of the last CM, the script to download the HepData tables should be implemented in a separate PR and not part of https://github.com/NNPDF/nnpdf/pull/1693 as mentioned in https://github.com/NNPDF/nnpdf/pull/1699.
The following is a slight improvement on the script initially introduced in https://github.com/NNPDF/nnpdf/pull/1500. It is working fine for some of the datasets I tried in https://github.com/NNPDF/nnpdf/pull/1684 and https://github.com/NNPDF/nnpdf/pull/1699 but people should try it.