[docs] [issue27504] Missing assertion methods in unittest documentation

[Ned Deily]

Changes by Ned Deily <nad at python.org>:


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nosy: +ezio.melotti, michael.foord, rbcollins
versions: +Python 3.6 -Python 3.2, Python 3.3, Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27504>
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