add callout triangle to north positioned tips
add callout triangle to north positioned tips

Caged/d3-tip,kbroman/d3-tip,ahmohamed/d3-tip,ninjaPixel/d3-tip,cgav/d3-tip,BI/d3-tip,looker/d3-tip,Crunch-io/d3-tip,brianally/d3-tip,chrisdibble/d3-tip,GerHobbelt/d3-tip,digitallumens/d3-tip,ONE-LOGIC/d3-tip,peterkshultz/d3-tip,kbroman/d3-tip,ninjaPixel/d3-tip