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Assert top-k parameter in __init__ method of Lunr is used.

Accelerate TfIdf in batches and enables to update TfIdf with new documents using the `add` method.

Add method `.to_csr()` and `.to_csc()` to TfIdf in order to speed-up the computation with large batch.

Disable tqdm bar of retrievers on demand using `tqdm_bar` parameter of `__call__` methods and `add` methods.

Speed up tf-idf by transposing the sparse matrix of documents in the `retriever.add` method instead of transposing the sparse matrix when querying.

Requirements update of Numpy and Scikit-learn dependencies version.