Pretty class as alternative for Show class

[Christian Maeder]

John Meacham wrote:
> Because then the same code will work with any of the pretty printers out
> there, Strings, and ShowS directly. It is an abstract type. I also have
> ones that spit out html and one that spits out ascii text along with a
> function that goes from screen position to what was used to create it so
> you can find out what people clicked a mouse on.

Browsers break html-code for you, but the most important part (namely to
compose vertically if horizontally does not fit into the width) is
missing from your DocLike class.

(Producing strings is no problem for any pretty printer library.)

Christian