Bar graphs

In this section we show you the basic features of bar graphs in PyX. All
examples shown here use the same data from `minimal.dat` available for download
at the first [minimal bar-graph example minimal.html].

Note that bar graphs differ from other xy-graphs in that they use ''discrete
axes'' for one graph dimension. However, the only affected components of this
fundamental change are one of the axes, which needs to be come a discrete one,
i.e. a bar axis, and the usage of appropriate graph styles.