ENH more pythonic way to treat list of list of labels
# This is a combination of 10 commits.
# The first commit's message is:
ENH add multilabel accuracy based on jaccard index

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TST better way to test the normalize option

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ENH add zero one loss based on jaccard distance + TST systematic test of normalize

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DOC write narrative doc for jaccard and subset based metrics

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Fix some doctest bugs

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ENH make a new metrics jaccard_similarity_score instead of adding functionality to accuracy_score

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Update the documentation for the jaccard_similarity_score

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DOC improve explanation of jaccard score

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Update what's new

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DOC even better definitions
ENH add multilabel accuracy based on jaccard index