function medianSorted(sorted) {
    return quantileSorted(sorted, 0.5);
}
The [median](http://en.wikipedia.org/wiki/Median) is
the middle number of a list. This is often a good indicator of 'the middle'
when there are outliers that skew the `mean()` value.
This is a [measure of central tendency](https://en.wikipedia.org/wiki/Central_tendency):
a method of finding a typical or central value of a set of numbers.

The median isn't necessarily one of the elements in the list: the value
can be the average of two elements if the list has an even length
and the two central values are different.

@param {Array<number>} sorted input
@returns {number} median value
@example
medianSorted([10, 2, 5, 100, 2, 1]); // => 52.5