Ensure that diagonalization based linear solver doesn't
assume hermiticity. Now qualitatively consistent.

General thoughts:
    Working in linear span of S much better as far as
        non-negative components goes, but it greatly
        increases overlap of final wavefunction with
        ground state - not ideal
    Explicitly removing the ground state does not improve
        results, and increases the overlap, as well as
        making the hamiltonian non-hermitian
    Options 1 - 3 of linear system solver introduce no
        quantitative difference in results.

Ultimately, it seems the closer S to the unit matrix the better,
but orthogonality still a worry. Non-hermitian projection
operator still making me uncomfortable.

New option: REMOVE_GS_FROM_H
    Does what it says on the tin. Default off.