Working GTM Example

Build a working GTM example by trying to reproduce the results shown on
Svensén's PhD thesis on figure 3.2 (p. 43) using the GTM implementation
provided by Netlab 3.3 with a minor tweak to the function gtminit:
131c131
< sigma = min(sigma, PCcoeff(net.dim_latent+1));
---
> sigma = max(sigma, PCcoeff(net.dim_latent+1));