Documentation deeply revisited. New phrasing: line splitting versus line

breaking, consistent usage of splitting and split; simpler explanation for
break hints and new documentation for pretty-printing boxes.

Tabulation boxes get deprecated: this mechanism does not interact nicely with
the rest of the pretty-printing engine and should be completely revisited...


git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@16444 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02