[docs] [issue18758] Fix internal references in the documentation

[Serhiy Storchaka]

Changes by Serhiy Storchaka <storchaka at gmail.com>:


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dependencies: +Improve cross-references in builtins documentation., Improve cross-references in pickle documentation.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18758>
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