Add javadoc for streaming quantile
Add javadoc for streaming quantile

shaohua-zhang/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu,apache/incubator-datafu,apache/incubator-datafu,shaohua-zhang/incubator-datafu