Python part still needs to be fixed, almost there, compiles in clang again

Add some forceeval and type double where possible

Thought it would maybe help with compilation

But not clear why this changes anything...

Fix missing inline

Added multipolar terms; doesn't compile on mac anymore

Appears to be working, additional testing required. Generalizing to handle G&V and G&T correlation integrals remains

No warnings from teqp code, all from externals

Very subtle problem with handling derivatives at zero density

Closes #38

Closes #40

Helpful for debugging

Tests should pass again