New conda-forge package for sphinx-simplepdf fixes some windows issues

[melund]

We had a lot of trouble getting the weasyprint dependency of sphinx-simplepdf working on windows. We had dll issues (OSError: cannot load library 'gobject-2.0-0') which only resolved by manually installing GTK on windows.

But yesterday we made a conda-forge package sphinx-simplepdf, that seems to fix the problem for us. Now we can create working environments with sphinx-simplepdf.