Provide documentation about icub fingers coupling mechanism

[kouroshD]

I am trying to understand how the coupling of the fingers are handled in the firmware, but I was not able to find the related part in the repo's code. Please if possible, point out to the part of code that handles the decoupling of measures related to the iCub hand and fingers.
In case, there is a documentation on that, please let us know.

cc @pattacini @traversaro @S-Dafarra

[pattacini]

I don't know about the FW and/or the intermediate YARP layer responsible for streaming out the motor and joint encoders but, in any case, the method iCub::iKin::iCubFinger::getChainJoints() contains a possible replica of the code required for dealing with the coupling/decoupling.

In fact, the goal is to take as input the motor and/or the joint encoders (received respectively from the state and analog ports) and prepare a vector that needs to describe every single joint of the kinematic chain. Thus, getChainJoints() has to be aware of the coupling.