DRY
Define MO::Basis::LCAO#nuclear_attraction
Define AO::Gaussian::Contracted#nuclear_attraction
Define AO::Gaussian::Primitive#nuclear_attraction
Define PimitiveProduct#nuclear_attraction_integral
Remove an unappropriate spec
MO::Basis#core_hamiltonian should all be finite
Spec for PrimitiveProduct#auxiliary_hermite_integral

X recurrence relation
Fix PrimitiveProduct#auxiliary_hermite_integral
Use patched rspec-extations

Fix bugs around be_within matcher
Augment specs for R_{tuv}^{n} recurrence relations
Fix PrimitiveProduct#nuclear_attraction_integral
alias
Refactor hermitian_coeff
Refactor auxiliary_hermite_integral
Augment specs for hermitian_coeff
Define PrimitiveProduct#electron_repulsion_integral
Merge branch 'feature/primitive_product' into develop