Pretty print for the model class

[gvegayon]

Goal

We need to have a nice printout of the model class. Users should be able to quickly inspect what the model is without having to list all members of the model class.

Context

During the development of the tutorials, it became apparent the need for this feature.

Required features

• It should have the __str__() method (see this).
• It should print something like the following:

pyrenew.[Model instance]
Number of parameters: [a number goes here]
State of the MCMC: [run/not run]
Model components:
- [Latent process 1]
- [Latent process 2]
- [...]
First (k) parameters: param1, param2, ..., (omitting [N - k]).

Model components can be sort of an instance-dependent print implemented in a hidden function, e.g., _print_details().

Specifications

• __str__() method for the Model metaclass.
• _print_details() method for the Model instances.
• Update the tutorials to include the model prints.
• Add a test that check for the required cases (TBD).