Horizontal grid lines don't reflect useful y-values

[drewnoakes]

Currently the horizontal grid lines are positioned so that a given number fit evenly within the visible space.

It'd be nice if these lines could be used to track values on a scale, as is done in most charts. This is especially the case when the max/min y-values are determined automatically.

To do this well, an algorithm should find values on a scale that feels right to a human. The builder has an example of some code that does this reasonably well.