This crate defines a
[Wadler-style](http://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf)
pretty-printing API.
Start with the static functions of [Doc](enum.Doc.html).
Let's pretty-print simple sexps! We want to pretty print sexps like
```lisp
(1 2 3)
```
or, if the line would be too long, like
```lisp
((1)
(2 3)
(4 5 6))
```
A _simple symbolic expression_ consists of a numeric _atom_ or a nested ordered _list_ of
symbolic expression children.