[latexrefman] Added trivlist

[Karl Berry]

    I added trivlist.  

Cool.

    I put it below list, but maybe it should be a
    separate environment?

A separate section. Yes, maybe so, since right now it is the only
environment done as a subsection. But it does seem logical as a
subsection. I left it.

In your two-item trivlist example, is it simple to say by what amount
(parameter) they are vertically separated?

> This example outputs the items as two paragraphs, except that (by
> default) they have no paragraph indent and are vertically separated.

    I also accidentally deleted \item so I ended up
    rewording that a small bit.

Of course such "deletions" are recoverable, but the current text looks
fine.

I made some tweaks to all the new text (and some of the old). I took it
on myself to reformat the environment examples in a way I find more
readable. Sorry.

    left edge of the label is at
    \leftmargin+\itemindent-(\labelsep+\labelwidth).  

I had no idea :). Which list parameters actually take effect has always
baffled me. One big problem is that (I believe) every *font* change
calls \@listI, which resets \topsep (and others?) to defaults. So merely
changing \topsep with \setlength turns out to have no effect. Or so it
seemed to me when I looked into it at one time. (I thought I had put
this into latex2e.texi, but I guess not.) The notes I have about it from
my document (the TUG interview book), for what it's worth:

  % http://www.tex.ac.uk/cgi-bin/texfaq2html?label=complist incomplete. xx
  % This seems to be the only way to change \topsep.
  % This \@listI macro is called after every font change.
  % \parsep and \itemsep could be changed after starting the environment,
  % but may as well change them here.
  \def\@listI{\leftmargin\leftmargini
              \topsep=\ivlisttopsep
              \parsep=\topsep  \divide\parsep by 2
              \itemsep=0pt plus1pt}%


Sadly, I ran out of energy going through the new list text. I hope I'll
get back to it soonish. I think the list of equations in the text, that
is, the paragraph starting with "Vertical spaces:", would be more
readable if each equation started on its own line. Maybe @table @math.

In general: I think it would be good to write ChangeLog entries
(especially) and also NEWS items as changes are made, so that making a
release doesn't require going through all the changes ... --thanks,
karl.

P.S. Another thing to do: go through and fix the overfull hboxes, and
maybe the worst underfull ones. Maybe \hbadness should be increased even
more if we don't want to fix all the underfull ones.