With these changes it is possible to set a custom spline interpolation
by giving a valid d3 interpolation to spline.interpolation.type.

Fixes #479

Add the ability to prevent elements from the showing up in legend and tool-tip

Enforcing the AMD factory standard

Add chart.api ($$.api) to 'onunselected' callback

Patch for #1141

Update tooltip.js

Fix whitespace in README.md

Merge branch '1033_custom_legend_config' of https://github.com/davidpoore/c3 into davidpoore-1033_custom_legend_config