Fix vertically overlapping value and row labels

[leeper]

trafficstars

The current binning algorithm simply puts labels on new lines when they're too close. A better version would evenly space the numbers within the range of overlap. It will have the same even appearance, but probably line up better with slope lines.

[leeper]

The new draw approach used as of https://github.com/leeper/slopegraph/commit/69f6143913fe524f062b5f49a55a357cb96f5f2c eliminated binning altogether. Will need to think of a new way to do this by, possibly, modifying y-values that are near to one another in the segmentize()'d matrix.