Configuring Chart Axes
 
 The vdl-chart-axis element has several possible attributes:  
 
- axis: This string value can be set to x or y
 - min: The minimum bound for the axis – it must be specified if you are using the max attribute
 - max: The maximum bound for the axis – it must be specified if you are using the min attribute
 - step: The step increment for the axis
 - unit: The unit for the axis, e.g. cm
 - type: A string that can be set to linear, log, date or category (default unless all series are of type scatter/line, when it defaults to linear)
 - title: A string used as a title for an axis, which can be a dynamic expression
 - show-grid: A boolean, defaulting to true, which controls whether or not a background grid is rendered – this can also be the result of a dynamic expression
 
 The above attributes can give rise to VDL charts defined, for example, as: 
 
                <vdl-chart>
  <vdl-chart-axis axis=”x” 
                  min=”0” 
                  max=”100” 
                  step=”20” 
                  units=”cm” 
                  type=”category”/>
  <vdl-chart-axis axis=”y” 
                  min=”0” 
                  max=”100” 
                  step=”20” 
                  units=”cm” 
                  type=”category”/>
</vdl-chart>
 
