Add GridLine.
Add style argument to Tex#line.
Add Tex.line (will eventually replace tex#line).
Changed GridLine#render to use Tex.line.
Add XTick.

Ticks are the marks on a chart's axes.  They typically include a label
and, for ticks on the x axis, a vertical grid line.
Add Axis.
Reformat some unit tests.
Allow . to match newline.
Add additional requirements.
Experiment with finer grained objects.
Remove experimental finer grained objects.