Breaking changes in control libraries

[domire8]

Knowing that some of the initiatives require breaking changes across the stack, it's possible to think about which breaking improvements we want to make in control libraries too. First and foremost, we need to look into the robot model library and think about how we can improve its usability and feature set to leverage pinocchio better and to potentially account for types of robots that are not just a chain of revolute joints.

• Improve Inverse Kinematics #205
• Add functionality to create a robot model from xml string rather than filepath #200
• Extract transforms between two frames from robot model #126

Apart from that, we can also try to address already existing issues:

• [Conflict] - Namespace robot_model #203
• Add integrate and differentiate methods to States #193
• Construct and convert CartesianPose from rotation or transformation matrices  #146

[eeberhard]

I think the way #193 is implemented, it shouldn't be ABI breaking. It adds contents to the header file but doesn't change the order or visibility of existing symbols, nor change any inline or template definitions.

I agree that in general, improving the robot model class would be the most valuable breaking change.