- Adds new algorithms to solve Lyapunov equations: Doubling algorithm and...

- Adds new algorithms to solve Lyapunov equations: Doubling algorithm and Square root solver. Their respective names are "doubling" and "square_root_solver".
- Adds the tolerance criteria for the iterative solvers (sylvester_fixed_point_tol, lyapunov_fixed_point_tol and lyapunov_doubling_tol)
- Updates the reference manual