gemdoc command for bash and zsh.

## gemdoc
if ( which "gem" >/dev/null ) ; then
  gemdoc() {
    for e in lynx w3m elinks links /usr/bin/open ; do
      if ( which $e >/dev/null ) ; then
        HTML_OPEN="${e}"
      fi
    done
    
    $HTML_OPEN `/bin/ls -1t $(gem env gemdir)/doc/$1*/rdoc/index.html | grep "\/$1\-[0-9]" |head -1`
  }
fi