debugged Floren-Zmirou and Martingale
1) fixed the h_n versus x_hn versus half_xhn issues
2) floren-zmirou estimator now correctly approximates the standard
deviation estimate as intended (squaring it gives us the variance)
3) Euler Maruyama is now a martingale (mu must be set to be greater than
1) (i.e. it most likely will be a bubble.)
Debbugs