Full `mlpack` support

[BERENZ]

Support for mlpack in:

1. lsh functions

• deduplication (the same dataset, given by x)
• record blocking with two datasets given by x, y
• blocking from saved index
• saving and reading index

2. knn functions

• deduplication (the same dataset, given by x)
• record blocking with two datasets given by x, y
• blocking from saved index
• saving and reading index

[BERENZ]

I do not know how to save objects from mlpack.