replacement for titlepage and more metadata commands

[Patrice Dumas]

Hello,

Here is a proposal to move on on the @titlepage redesign, which is mainly
based on Gavin ideas in
https://lists.gnu.org/archive/html/bug-texinfo/2019-03/msg00029.html

I propose to add a @documentinfo block which would contain information
that can be used for diverse purposes, but in particular to do the formatting
previously assigned to @titlepage.  It would include
1) already existing @-commands, such as @title
2) a new block commmand that corresponds the the current content after the
  first @page of @titlepage that I propose to name @publicationinfoextra
  (is @titleverso in Gavin mail).  It could be generated automatically
  if not present.
3) we could, optionnally, add a new block @-command that would allow to
  format the cover, corresponding to the current @titlepage content before
  the first @page.  It could be named @cover.  Using @cover instead of
  providing enough metadata such that the cover can be automatically formatted
  would be discouraged in the documentation.
4) optionnally, more metadata @-commands, maybe only in a second step, and
  in particular a generic metadata @-command that, in my opinion, is missing
  from the Texinfo language.

@titlepage would also remain to be backward compatible, but would be
interpreted as the new @-commands.

Any comment on the general scheme and on the inclusion of 3) and 4)
optional features (that I think we should include)?

-- 
Pat