[Enhancement] Weighted Median function

[hado0601]

Hi, there is also a concept of weighted median. I think it'd be really nice to have it in bottleneck.

Ideas: https://en.wikipedia.org/wiki/Weighted_median, which also contains O(n\log n) algo.

C/Python Implementation: https://github.com/FilippoBovo/robustats
Python only (list/ numpy) implementation: https://github.com/tinybike/weightedstats

Thank you very much,

[Mickychen00]

Second this feature.