Fixed Hierarchical code for ratio_hierarch, generator memory curves

- Added: Ratio_hierarchical parameter, allows to set the ratio of layer two to layer one. If high, high number of layer two.
- Fix: Empty compute_marginal_inverse_FI in hierarchicalnetwork. Might want to try computing it, at some point…
- Added: Generator for memory curve for a hierarchical code. Vary sigmax and ratio_hierarchical, in plausible ranges.