Improved handling of Symbolic input to kinematics code

Adjoint action code now performs 50-step simplification of symbolic forms (which eliminates several trigonometric combinations that matlab doesn't directly recognize as being equal to 1).

N_link_chain and Nonholonomic connection code are now more robust to mixed symbolic and numeric inputs (e.g., a chain with symbolic lengths for the links, but evaluated at a numerically-specified set of joint angles).