Feature Req: curveTangent node

[MartinoMadeddu]

Summary

Add the ability to simply and quickly calculate tangent and bitangent on sets of curves in the same fashion as we can do it on geometries with meshTangent.

This would greatly help with using OSLObject to do curve operations and deformations (once we have a tangent we can calculate local spaces, axis, angles etc in OSL)

thanks