docs: change `troubles` references to `instability` Per https://www.mercurial-scm.org/wiki/CEDVocabulary. There are a couple instances of 'troublesome' which probably need a word, as deriviatives of 'instability' didn't really fit. At least some of these are in the unlinked obs-terms.rst page.

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# name space package to host third party extensions

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from __future__ import absolute_import

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import pkgutil

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__path__ = pkgutil.extend_path(__path__, __name__)