releasenotes: add similarity check function to compare incoming notes
It is possible that the incoming note fragments have some similar content as the
existing release notes. In case of a bug fix, we match for issueNNNN in the
existing notes. For other general cases, it makes use of fuzzywuzzy library to get
a similarity score. If the score is above a certain threshold, we ignore the
fragment, otherwise add it. But the score might be misleading for small commit
messages. So, it uses similarity function only if the length of string (in words)
is above a certain value. The patch adds tests related to its usage. But it needs
improvement in the sense of combining incoming notes. We can use interactive mode
for adding notes. Maybe we can do this if similarity is under a certain range.
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https://www.mercurial-scm.org/wiki/ContributingChanges
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273ce12ad8f1` will report some style violations on a very old commit).