Ensure text contrast

[broadpeter]

All templates with directly labelling either on bars or beside data points should have options to ensure text contrast either

• ability to separately set text in config
• or text that automatically adjusts
  For example on bars, black or white text based on calculation of darkness of data using some code like this:

var color = .. function giving color of the bar ..
text.style("fill", function(d) { return d3.hsl(color(d)).l > 0.5 ? "#000" : "#fff" })

[henryjameslau]

Could use chroma.js to calculate contrast