Compute weighted percentiles. If the weights are equal, this is the
same as normal percentiles. Elements of the data and
wt arrays correspond to each other and must have equal
length (unless wt is None ).
 Parameters:
data (A numpy.ndarray array or a
list of numbers.)  The data.
wt (None or a numpy.ndarray
array or a list of numbers. All the weights must be
nonnegative and the sum must be greater than zero.)  How important is a given piece of data.
percentiles (a list of numbers between 0 and 1.)  what percentiles to use. (Not really percentiles, as the range
is 01 rather than 0100.)
 Returns: [
float , ... ]
 the weighted percentiles of the data.
