Modified credregion() to return the smoothed pdf, its X values, and the minimum density in the percentile-HPD region.  Finished the docstring.
Modified credregion() to return the smoothed pdf, its X values, and the
minimum density in the percentile-HPD region.  Finished the docstring.

pcubillos/MCcubed,pcubillos/MCcubed,pcubillos/MCcubed