[CHANGES] #docinfo and publisher variables, multiple changes

[Rob Beezer]

It has been a long road to get our heads properly around string parameters,
publisher variables, and #docinfo entries, to effect changes in behavior. But,
to mix my metaphors, there is light at the end of the tunnel. Thanks for
everyone's patience. This was all motivated by *finally* getting #docinfo
ship-shape in the schema.

A whole bunch of #docinfo enties have permuted or moved a bit, two move to the
publisher file, and one publisher variable moves to #docinfo. #5 below is the
most consequential for the code it seems, the @external directory is moving its
specification.

All of these should continue to honor the old forms, so none of this is urgent.
But you will get warnings.

How do we decide? A long back-and-forth discussion with my assistant arrived at
some principles, one write-up for authors and publishers, and one for developers.

Section 5.6: Customizations
https://pretextbook.org/doc/guide/html/processing-customizations.html#processing-customizations

Section 49.2: Choosing a Home for Configuration
https://pretextbook.org/doc/guide/html/developer-configuration-homes.html#developer-configuration-homes

CHANGES:

1. docinfo/programs -> move inside new docinfo/defaults
2. docinfo/parsons -> move inside new docinfo/defaults
3. docinfo/defaults/image-width element -> attribute form:
<image-width>60%</image-width> -> <images width="60%"/>
(new: @margins may accompany @width)
4. docinfo/event -> frontmatter/bibinfo/event
5. publication file source/directories/@external
-> docinfo/directories/@external
(@data was already there; paths still relative to main source file)

PUBLISHERS (publication file edits)

6. docinfo/brandlogo -> /publication/html/brandlogo
(same attributes: @source required, @url optional)
7. docinfo/images/archive -> /publication/html/images/archive
(same content and @from attribute)
8. source/directories keeps @generated ONLY; delete @external after step 5

NO ACTION, BUT VALIDATION IMPROVES

9. Now schema-valid: docinfo elements "directories", "doenetml", "logo";
"blurb" and "document-id" promoted from dev schema to stable
10. Now schema-invalid (deprecated years ago, long ignored):
docinfo/feedback, docinfo/numbering -- delete them

NOT HONORED / HARD EDGES

11. A "brandlogo" without @source was always invalid and rendered a broken
image; it is now simply invalid -- supply @source or delete

See also:

Section 4.25: Document Information
https://pretextbook.org/doc/guide/html/topic-docinfo.html#topic-docinfo

[Rob Beezer]

A follow-up, I missed one natural change that should have been in this batch:

docinfo/cross-references/@text -> docinfo/defaults/xrefs/@text

Old: <cross-references text="type-global"/>

New: <defaults>
<xrefs text="type-global"/>
</defaults>

The old form still works, with a deprecation warning. This was the last
document-wide default for an authored attribute living outside "defaults".

Rob