Add cstdio include.
Update use of sym-ildl factorization.
Pass L as a lilc matrix to linear solver.
Add solve_lower_triangular.
Custom triangular solver.
Custom lower-triangular transpose solver.
sym-ildl functions moved to templated function.
Newton solver parameters as enm classes.
Faster transpose sym-ildl solve.
Use Eigen as sparse linear solver.
Fix some warnings about unavoidable conversions.