[Style Guide] Update to include numpy -> jax guidelines

[mmcky]

@jstac has made some good comments via email.

1. Let's replace (numpy with jax). IMO, we should provide simple, clean implementations of economic models, using the best library at the time.

I'd like us to also settle around a relatively uniform style, based around JAX style functional programming -- pure functions, no side effects.

Primitives stored in a class Model(NamedTuple) object...

@HumphreyYang I will draft something up for our style guide. If you can think of other things to add to the style guide I will do a round before Monday's meeting.

[mmcky]

Some additional notes to think about when updating the style guide

--- @jstac

Let's also have in the back of our minds that we want to break up classes and methods into

• a short class Model(NamedTuple) with primitives and no methods
• a function create_model_instance that generates instances when necessary and
• a collection of functions of the form def func(model: Model, data) that do the heavy lifting.

One advantage is that we'll follow the JAX model of functional programming as a de facto style guide.

Another is that we'll break up large classes, which tend to be harder for readers to digest.

Of course Tom should be consulted as necessary