implement params_dict method or attribute

[aloctavodia]

Currently, if we have a distribution and want to find out its parameters programmatically we can do:

• dist.params, a tuple with the values
• dist.param_names a tuple with the names

For distributions with more than one parameterization, these two functions will return the values and names of the default/canonical parameterization. Additionally, we can obtain the values of the parameters by name, even non-canonical names, for example, this works pz.Normal(mu=0, sigma=0.5).tau .

I think we should have a params_dict attribute or method that returns a dictionary with names:values. Not sure which one is better

For distributions with more than one parameterization, what should we return?

• attribute. Just the canonical dict, a tuple of dicts with all parameterizations?
• method we can pass an argument to ask for different parameterizations like "canonical" vs "alternative". For distributions with more than 2 parametrization we need some other keyword... not sure what would be a nice choice.