Reimplement normalisation for the HashingVectorizer, add a testcase for that

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 25, 2021

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Use sparse CSR matrices to get scikit-learns behaviour. All tests pass

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 25, 2021

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Use the correct logarithm; IDF matrix matches

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 23, 2021

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WIP TfidfTransformer, works for #docs == 1

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 20, 2021

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Fix HashingVectorizer to work the same as scikit-learn. Extend test

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 16, 2021

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Impl HashingVectorizer, add (failing) test

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 14, 2021

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Initial patch. Impl iterator for n-grams

Created by  Gz5AN8tiLGjsQNTG24sqRr5jNodcDoAzyZSgZGoaYTaD  on July 14, 2021

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