stdio_filebuf docs

[Benjamin Kosnik]

>2002-02-04  Jonathan Wakely  <redi@gcc.gnu.org>
>
>	* docs/html/27_io/howto.html: New section on stdio_filebuf.
>	* docs/html/ext/howto.html: Move stdio_filebuf notes to 27_io.
>	* docs/html/documentation.html: Regenerate.
>
>I'll also added a link from the "Deriving a stream buffer" section to
>Dietmar Kuehl's iostreams page, but I'll do this as a separate patch.

Looks great! Thanks Jonathan.

-benjamin