Copy edit of UKF chapter.

Also found a mistake in the text about computing the residual
of angles that was duplicated in the EKF chapter, so I fixed the
error in that chapter as well.

I pulled out the 'track in a circle' example as it is the usual
sort of textbook nonsense problem that no one cares about. I created
an 'old-content' Notebook in case anyone still wants to see it; I
may put more content there as I continue to edit.

code/ukf_internal.py

@@ -381,7 +381,7 @@ def _plot_iscts(pos, sa, sb, N=4):
         plt.scatter(xs_a, ys_a)
         plt.scatter(xs_b, ys_b)
     plt.gca().set_aspect('equal')
-    plt.show()
+
 
 def plot_iscts_two_sensors():
     pos = np.array([4., 4,])
@@ -401,6 +401,7 @@ def plot_iscts_two_sensors_changed_sensors():
     plt.scatter(*sa, s=100)
     plt.scatter(*sb, s=100)
     _plot_iscts(pos, sa, sb, N=5)
+    plt.ylim(3.8, 8.5)
 
 
 if __name__ == '__main__':