There are three different types of Axes for line charts that project
their properties onto the axis type. I am trying to emulate that here.
If you specifically declare a LineChartAxis, then you MUST attach the
axis type. The library lets you play a little fast and loose with this,
but because we're going for some compile-time checks, the typing file is
going to enforce being specific.
Had to add some explicit typing to some of the example functions just to
get the test to complete successfully. Maybe that shouldn't be a
concern in the test files?
Matt Gibbs