For every struct, overload Base.show() and Base.summary()

## Issue
Some of the distributions and objects are very unwieldy especially when printing to terminal IO

## Possible Solution
Inspiration: @glwagner at Oceananigans.jl
- Providing `Base.show()` methods (and improving those that currently exist) would improve the user experience in the REPL.
- Also look into `Base.summary()` functions which can provide something cleaner than `nameof(typeof(...))` calls in error messaging etc.

Start by inventorying the distributions and objects that are unwieldy in terminal output, then inspect any existing Base.show methods and the relevant Base.summary behavior. Compare REPL output and error-message summaries for each struct; done means every struct has appropriately concise, useful display behavior.

Written by the indexing model from the issue text.