[docs] [issue21528] Fix a number of typos in the documentation

[Roundup Robot]

Roundup Robot added the comment:

New changeset 33f6e360826e by Donald Stufft in branch '2.7':
Fix Issue #21528 - Fix documentation typos
https://hg.python.org/cpython/rev/33f6e360826e

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue21528>
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