Format a bit of code for consistency.
Add SeparatorRenderer.
Add ItemRenderer.
Add XLabelRenderer.
Add FrameRenderer.
Add another ItemRenderer test.
Alter TeXGenerator to use (most of) the renderers.
Rename DateLabel to XLabel.
Save y_coordinate in XLabel.
Remove XLabel dependency on Settings.
Save y_length in XLabel.
Remove XLabel dependency on Chart.
Revert "Remove XLabel dependency on Chart."

This reverts commit 32b28e51173ee4b86d8c290d9619bcdca719ca47.
Revert dependency removal.
Add settings to Chart.
Remove XLabelGenerator direct dependency on Settings.
Remove chart parameter to XLabelRenderer#initialize.
Change TeXGenerator to invoke #render on XLabel instances.
Remove settings parameter to ItemRenderer#initialize.
Add RendererFactory#item_renderer.