Fix: bug with threshold helper labels

Referenced in issue: #78

Fix: bug in color legend updating

A reference to this bug: #69

Huge thanks to @hanneskuettner for making a pull request for this.

Fix: Previously inconsistent label offset from size line legends

Fix for this issue: #73

Added Locale Support on all Legend Types

Addressing this issue brought up by @LaCroute #68

With a follow up via pull request to implement this feature. #71
Thanks Clément!!

Upgrade to d3 v4

Latest docs for the new version.

Docs for the previous version of d3-legend.