Hyperboloid model: incorporate subjective time aspect

[drbenvincent]

It has been shown by Takahashi (2016) that exponential discounting of logarithmic scaled time (i.e. Weber's Law)

t(delay) = b.In(1+a.delay)

is equal to this hyperboloid discount function

1/(1+a.delay)^(k.b)

We cannot identify k.b on a discounting only experiment, and the hyperboloid discount function we use is

1/(1+a.delay)^S

and so the corresponding inferred subjective time function is

t(delay) \propto S.In(1+a.delay)

• [x] The Hyperboloid class should be moved to be a subclass of SubjectiveTimeModel
• [x] We also need a SubjectiveTimeWebber class (subclass of DiscountFunction) so that we get this Weber's Law plotted in the 'experiment' multi panel plot