I chose “setupcfg” as prefix instead of “packaging-setupcfg” because the scope
of the spec is not limited to packaging: it’s intended as a language-agnostic
document for packaging tools developers as well as Python authors.

I tried shortening the sidebar ToC with the tocdepth option instead, but it has
a bug which caused all headings with a level deeper than the tocdepth value to
all have the same section number, which was a usability regression rather than
in improvement.

I reworded “wizard” because it is a Windows-specific term.

Also beautify import lists.  Having them grouped by lenght makes it slightly
easier to look for a module.

I have removed the reST target I added in 38cdca2cc253: it is not necessary, as
people can link to the glossary entry or the abc module without it.

Two indentation fixes from 3.2 collections.rst have been ported to 3.3
collections.abc.rst.

- Rename reST target name for collections ABCs to avoid collisions
- Add link to importlib ABCs (collections, numbers and io ABCs were already
  linked)
- Link to glossary entry from numbers module doc (other modules already do it)

test_multibytecodec_support. Improve also error message of the
test_errorhandle() of TestBase.

test_multibytecodec_support. Improve also error message of the
test_errorhandle() of TestBase.

The previous markup hijacked the abstract-base-classes glossary entry,
which resulted in the HTML linking to collections.abc when defining the
generic ABC concept.  Now the glossary links to the abc module.

I’m afraid my docstring is not as clear as it should be, but I can’t
find a concise way of describing what the code does.  Suggestions for
improvements welcome.

Keep a timeout of 1 hour for buildbots.