I added a link from the term “virtual subclass” to the glossary entry
for ABCs but this was not enough, now the glossary briefly defines
“virtual” and links to the abc module doc which contains more mentions
of virtual subclasses.

Suggested by Terry J. Reedy.

``code`` markup is enough to mark command-line fragments or to talk
about a character.  ``'c'`` is still used for actual Python string
objects.  I did a similar change in optparse.rst in r86521.

I’ve also ported two minor changes from the 3.3 version of the file
(removing an unnecessary module name in a class directive, adding a
comma).

The example version numbers were invalid and “package” was misused.  I
also made lines shorter, replaced “e-mail” with “email” (more common in
the stdlib and I believe in English generally) and tweaked a few other
things.

I made the doc for the compat alias BadZipfile shorter and used a
directive to document deprecation.

I figured there was no point of talking about zipfile.error (“the old
name” that’s older than the other old name BadZipfile) in the 3.x docs
so I just removed it.

Use startswith, instead of ==, when testing sys.platform to support
new platforms like Linux 3 or OpenBSD 5.