[v3] allocator documentation revamp

[Benjamin Kosnik]

>2004-02-25  Jonathan Wakely  <redi@gcc.gnu.org>
>
>	* docs/html/20_util/howto.html, docs/html/20_util/allocator.html,
>        docs/html/ext/howto.html, docs/html/ext/mt_allocator.html:
>        Fix markup, more <link> tags.
>        * docs/html/documentation.html: Regenerate.

looks good, thanks