[gentoo-doc] adding support for wikipedia links

[Mike Frysinger]

often when i'm writing docs i like to throw in links to wikipedia as it 
contains a wealth of information that i dont even want to try to duplicate

rather than having to do like <uri 
link="http://en.wikipedia.org/wiki/Foo">FOO</uri> all the time, would it be 
possible to get a new tag implemented ?  say something like:
<wikipedia topic="Foo">FOO</uri>
-mike