[New model] Add Hunt1959

[chrisleaman]

Who is the published the model and in what year?
Hunt (1959)

Please provide a link, doi or citation to the paper
I haven't been able to find the actual paper, but this is the reference that is commonly used:
Hunt, I.A., 1959. Design of Seawalls and Breakwaters. Journal of the Waterways and Harbors Division 85, 123–152.

Any other details that would be useful?
For example:

• Hunt formula uses Rmax, probably need to use a seperate Rmax parameter so it doesn't get confused with R2
• From Atkinson et al. (2018):