existing files should be overridden when build sphinx-docs

Created by: wilsonmr

I think we should change https://github.com/NNPDF/nnpdf/blob/f9f753b1a7e1ad579b5ef686ed6f3bb229cde4e6/doc/sphinx/Makefile#L20

to be

sphinx-apidoc -f -o ./source/modules/validphys ../../validphys2/src/validphys/ ; 

adding the force option so that if a new module is created, for example in validphys.scripts then the docstrings are properly indexed even if docs have previously been built.

Unless there is an obvious downside?