Proposal: literature review suggests ZhangWang algorithm

[ljw1004]

I read this literature review:

• 2020 A survey of approximate quantile computation on large-scale data (technical report) (by Chen, Zhang)

It points to another paper, which it claims has 60x-300x speedup over the "GK01" implemented in this crate, and claims it has state-of-the-art space upper bound:

• 2007: A fast algorithm for approximate quantiles in high speed data streams (by Zhang, Wang).

It would be awesome to implement the ZhangWang algorithm for this crate! The algorithm outlined in the paper look kind of appealing. (I was going to implement it, then got sidetracked by benchmarks #32 and never got any further...)