add the fermi surface database

execute.py

mkdocs.yml

src/fermi_surfaces.md

src/scripts/x3dom.js

src/x3d/Ac.x3d

src/x3d/Ag.x3d

src/x3d/Al.x3d

src/x3d/Au.x3d

src/x3d/Ba.x3d

src/x3d/Be.x3d

src/x3d/Ca.x3d

src/x3d/Cd.x3d

src/x3d/Cd_fcc.x3d

src/x3d/Co_fcc.x3d

src/x3d/Co_fccdn.x3d

src/x3d/Co_fccup.x3d

src/x3d/Co_hcp.x3d

src/x3d/Codn.x3d

src/x3d/Coup.x3d

src/x3d/Cr.x3d