TODO: Heston Documentation

[lacagninag]

TODO: Heston Documentation

With the aim of clarity in the documentation of the Heston model we report here a list of phrases or formulas to rewrite as soon as another modification will be done to the codebase.

• Use always \mathbb{P} to indicate probabilities;
• Use Z_1, ... Z_n instead of N(0,1)_1 to indicare normal random variables.
• Add Forward Starting Digital