Implement Limb Class to be used in RobotBase

[jdcaporale]

Need a limb class LimbBase that can be used by RobotBase
First version:

• Eigen:VectorXf ForwardKinematics( ... )
• Eigen:MatrixXf Jacobian( ... )
• Eigen:VectorXf InverseKinematics( ... )
• struct LimbConfig
• LimbConfig config
• std::vector<std::shared_ptr<JointBase>> joints
• virtual void Update()
• helper functions and members
• a clean 3DOF example

Future Versions:

• std::vector<Eigen::Vector3f> jointFrames
• Allow optimize of Jacobian and FK using jointFrames or upgrade to ValidatedCache
• General FK, Jac, IK Test Functions?

Far Future?:

• "upgrade" to DH parameters maybe
• URDF?
• anything else?