Added scfint.py with tools for analytic lattice-sum integrals.
Added scfint.py with tools for analytic lattice-sum integrals.

gkc1000/pyscf,gkc1000/pyscf,sunqm/pyscf,sunqm/pyscf,gkc1000/pyscf,sunqm/pyscf,sunqm/pyscf,gkc1000/pyscf,gkc1000/pyscf