per-package documentation in on-line help system

I've committed some code to bring per-package (share packages, that is)
documentation into the on-line help system. As with the general
documentation, per-package stuff is written in Texinfo and compiled to
.info, the .info is searched to build an index, and the index is
searched at run time for the ? and ?? commands.

So far the scheme is not fully automated -- makeinfo, build_index.pl,
and load(my_index) all have to be executed by hand. Let's talk about
suitable ways to automate this stuff.

This code is committed to the master branch, so it won't be in any 5.29
release. I brought this stuff out of cold storage in response to a
message about a system to parse comments for documentation. For the
record, I think it's a good idea to keep documentation with the package,
but it's better to use the existing Texinfo system instead of rolling
our own documentation parser.

As an example, I've updated the existing abs_integrate.texi (in
share/contrib/integration) with Texinfo stuff to generate a table of
contents. 

  cd share/contrib/integration
  makeinfo abs_integrate.texi
  perl ../../../doc/info/build_index.pl abs_integrate.info > abs_integrate-index.lisp

and then in Maxima:

  load ("abs_integrate-index.lisp");
  ?? _integrate

and so on to read the documentation.

Hope this helps,

Robert Dodier