This work is based on "Space-Efficient Online Computation of Quantile Summaries" by M. Greenwald and S. Khanna (known as GK-algorithm) http://infolab.stanford.edu/~datar/courses/cs361a/papers/quantiles.pdf
Also ideas for the implementation are taken from http://www.mathcs.emory.edu/~cheung/Courses/584-StreamDB/Syllabus/08-Quantile/Greenwald.html
tt := gkquantile.NewGKSummary(0.025) // where 0.025 is an accuracy. Smaller value gives a better accuracy, but will require more storage
tt.Add(value) // add as much values as you want
tt.Query(0.95) - receive 0.95 quantile
tt.Query(0.50) - receive 0.50 quantile (median)