DBSTREAM: custom weights

[th3sh3ph3rd]

Currently, in DBSTREAM all new data points are uniformly weighted with weight 1. This is also in line with the algorithm from the original paper.

However, for many applications it would be useful to have the option for custom data point weighting. This would also be supported by DBSTREAM.learn_one(), which foresees a currently unused parameter w.

Some minimal changes to the DBSTREAM code would strongly increase value and versatility of the implementation.

If it is decided that this additional feature is useful, I would be open to contributing the necessary changes to the code base.

[MaxHalford]

Sounds like a good idea! Feel free to propose an implementation.