% Quantization of x.
%
% INPUT
% -----
%
% Several options are available as optional parameters, listed below:
%
% - 'centroids' : centroids to use. Default is []. If non-empty, all other
% parameters are ignored.
%
% If 'centroids' is not provided or empty, uniform quantization will be
% done. Parameters then are:
%
% - 'border_method': either QUANTILE (default) or ABSOLUTE
% - 'border_param': parameters for borders. depending on borders_method:
% * border_method==ABSOLUTE: the actual min and max value to use
% * border_method==QUANTILE: the quantiles to use for min and max.
% default is [0.1,0.9]
% - 'control_method': either 'RATE' (default) or 'DISTORSION'
% - 'control_param': parameter for quantization step. depending on
% control_method:
% * control_method==RATE: number of quantization cells
% * control_method==DISTORSION: size of quantization cells.
% - 'display': 1 or 0, whether or not to display some figure
%
% OUTPUT
% ------
% - xbar: quantized signal
% - misc: a structure containing the following fields:
% * centroids: the used centroids. min and max are the first and last
% ones, respectively
% * group: for each data point, gives the index of the selected
% centroid
% * delta: only there if centroids were not provided: selected
% quantization step
%--------------------------------------------------------------------------
% Antoine Liutkus, Inria, 2016