[CHANGE] Numbering options, especially for "project-like"

[Rob Beezer]

I am working on how PreTeXt computes the numbers of objects, specifically blocks
right now. This will allow some new (limited) flexibility.

"Running on distinct counters" has been experimental for certain objects.
Undocumented switches, #docinfo configuration, publisher file entries. Now all
of this is unified, and documented, as publisher file entries. So the
hodgepodge of old ways are deprecated, and we have new ways via publisher
variables. We will try to honor your intent until you switch over.

One big change, which has been telegraphed previously - PROJECT-LIKE (#project,
#activity, #exploration, #investigation) were first made to default to their own
counter, but now the default is to not use distinct counters unless explicitly
elected in the publication file. The advice has been to use the old #docinfo
setting and set it to prescribe the distinct counters. If you did that, you
will be fine until you switch over.

The publisher switches are in now, new code for numbering is close to being
finished.

Documentation, start at:
Section 44.2: Numbering Options
https://pretextbook.org/doc/guide/html/publication-file-numbering.html#publication-file-numbering

Questions may be answered with the Best Practice:
Best Practice 26.3.1: Use Separate Counters Sparingly
https://pretextbook.org/doc/guide/html/publisher-numbering.html#best-practice-distinct-counters

Rob