The original author of most of the code needed to implement this was
brian d foy, who sent this module to me after I complained I didn't have
the time to implement horizontal bar charts. I took the code that lived
in here, and distributed it over axestype.pm and bars.pm, to allow for a
better integration all around. His code, in turn, was mainly based on an
earlier version of bars.pm and axestype.pm.
