[WIP] GIFT gaussian elimination testing

[yut23]

I ported the Fortran code to Python, then added some C++ and Python codegen for us to play with.

It's currently set up to generate code for aprox13. With the current array ordering (species then enuc), it produces the same code as a non-sparse matrix (1118 statements), but if we move enuc before the species, it's a lot better at 302 statements.

[BenWibking]

For future reference, the original method paper:
Gustavson, Liniger, and Willoughby. "Symbolic Generation of an Optimal Crout Algorithm for Sparse Systems of Linear Equations." JACM (1970) https://dl.acm.org/doi/pdf/10.1145/321556.321565.

They claim that in typical cases, the complexity goes from $\mathcal{O}(N^3)$ to $\mathcal{O}(N^2)$.