[latexrefman] Add Arrows subsection

[Karl Berry]

    I'm not so sure how they would use that information. 

I sometimes want to know a Unicode code point for a variety of reasons
-- what &#xxx; to put into a html file,
what code block it's in so I can look up similar symbols,
to discern the UTF-8 bytes in which it is expressed,
..

    Maybe I just have in mind an American LaTeX user. :-)

Well, math knows no language :). But, even as an American, I do often
want to know the code point for random "foreign" symbols or letters.

    Just figured I offended svn in some way.

svn doesn't take offense, it just does what it's told :).
Will try to figure out what's going awry, eventually ... --thanks, karl.