made grid = True by default for plot()
* removed stacked 3d bar charts
   they are too buggy and unlikely to work any time soon (see https://github.com/matplotlib/matplotlib/issues/155/ and https://github.com/matplotlib/matplotlib/issues/1292/)
 * further cleanup/simplify charting code (in part thanks to the removal of stacked bar3d)
kill commented code and add docstring
more work on the charts documentation
more work on the charts documentation
kill bar3d entirely, it's too buggy
kill bar3d from the doc
move ndim() to utils
updated changelog for the prerelease
updated versions for the prerelease