ENH: rename, or at least alias, "quantile" method with "fractile"
#### Is your feature request related to a problem?

The method called quantile, is misnamed. What is it calculating is the fractile. A fractile is a number, where fractile(x) = percentile(100x).  A quantile is  a set of fractiles.


#### Describe the solution you'd like

Fractile becomes an alias of quantile in next non-major release then quantile is removed in next major release, or redefined. An appropriate redefinition would take an integer n, and return an array of  n values where the kth value is given by fractile(k/(n+1)) as per https://en.m.wikipedia.org/wiki/Quantile

#### API breaking implications

Removal or redefinition of quantile method will of course not be backwards compatible. 
