Further diffusion models to include

A potential list:

- NIU - Easingwood et al. 1983. A Nonuniform Influence Innovation Diffusion Model.
- Logistic model
- Weibull model - done
- Gamma model
- GMB - Bass, F.M et al. 1994. Why the Bass Model Fits without Decision Variables.
- Trapezoids and Triangles - Hu et al. 2018. Forecasting New Product Life Cycle Curves: Practical Approach and Empirical Analysis