

This is a modified version of the code generator from libcint
which supports analytic FT with combinations of select one-electron operators.

To add new integrals, just add new entries to "auto_ft.cl" and then run
`clisp auto_ft.cl`. Refer to the libcint documentation here:
https://github.com/sunqm/libcint

The current integrals have been validated; always check new ones
for correctness. There may be some uncaught bugs.

Only the various flavors of p and r are supported.
No nuc, rinv, nabla-rinv, g, gaunt, breit, etc.
Dot works, but cross products do not.

The resulting integrals may be used for both molecular and PBC (lattice sum)
ft-aopair. See pyscf/gto/ppnl_velgauge.py and pyscf/pbc/gto/pseudo/ppnl_velgauge.py
for examples.

