[issue12301] Use :data:`sys.thing` instead of ``sys.thing`` throughout

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

Changing ``x`` to :data:`x` adds 4 chars.
Changing ``x()`` to :func:`x` justs adds 2.
If I were to review, I would prefer that the additions not trigger cascading line rewraps.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue12301>
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