Keeps track of the longest key and value in a hash, letting you
retrieve them later.  Avoids having to scan the entire hash when
at all possible.

I wrote this in response to a discussion on perlmonks, which you
can find here:
    http://www.perlmonks.com/index.pl?node_id=285305

To install, do the usual dance:
    less Makefile.PL
    less lib/Tie/Hash/Longest.pm
    less test.pl
those being to ensure that I'm not being evil, then:
    perl Makefile.PL
    make
    make test
    make install
