wrap paragraphs to fit into the screen

this patch wraps paragraphs and block quotes to fit within the terminal.
(similar to how man pages do it) it also indents paragraphs by 2 chars,
This makes markdown much more readable, especially if someone has not wrapped
the source nicely.

I also wanted to do this for lists, but it wasn't that easy to add to your
list processing code, so I thought I'd run this by you first.

my main case is to make nodeschool problems more readable (/cc @rvagg)