Add example for Q^X

examples/valmari-fig3-rational

+# This is Figure 3 from "Simple O(m log n) Time Markov Chain Lumping"
+# by Valmari and Franceschinis.
+{B1, B2, B345, B6}x(Q^X)
+
+# elements of the same block are numbered from top to bottom
+b6_1: (B6  , { b3_2: 1.0 })
+b6_2: (B6  , { b4: 1.0 })
+b3_1: (B345, { b1: 1.0 })
+b3_2: (B345, { b1: 1.0 })
+b4:   (B345, { b2: 0.5, b5: 0.5 })
+b5:   (B345, { b5: 1.0 })
+b1:   (B1  , { b1: 1.0 })
+b2:   (B2  , { b2: 1.0 })

examples/valmari-fig3-rational.out

+Block 0: b3_2, b3_1
+Block 1: b1
+Block 2: b2
+Block 3: b6_1
+Block 4: b5
+Block 5: b4
+Block 6: b6_2