Add Exercise 10.1.
Add Exercise 10.2.
Add Exercise 10.3.

WIP.
Add Exercise 10.4.
Add Exercise 10.5.

WIP.
Add Exercise 10.6.
Exclude extra entries when computing W_sr, A_kr.

Extra entries may be present in the kinematic differential equations and
velocity constraint maps for use in substitutions. Exclude extra entries
when computing the matrices W_sr, A_kr.
Add Exercise 10.10.