Function percentile

Output the percentile(x) It is simply using the nearest-rank method, cfr. Wikipedia but it will only keep an ordered list of the n largest elements so far, which means that computing the 90th percentile only needs to keep 10% of all the values seen in memory, but the 50th percentile needs a buffer of 50% of all values.

Various 'streaming' implementations exist, but they are more complex, so ... maybe later.

Example

   pipe(
     itr8Range(1,100),
     percentile(95),  // => [ 95 ]
   );