added Viterbi algorithm (#1099)

* changed queue to set in AC3

Changed queue to set in AC3 (as in the pseudocode of the original algorithm) to reduce the number of consistency-check due to the redundancy of the same arcs in queue. For example, on the harder1 configuration of the Sudoku CSP the number consistency-check has been reduced from 40464 to 12562!

* re-added test commented by mistake

* added the mentioned AC4 algorithm for constraint propagation

AC3 algorithm has non-optimal worst case time-complexity O(cd^3 ), while AC4 algorithm runs in O(cd^2) worst case time

* added doctest in Sudoku for AC4 and and the possibility of choosing the constant propagation algorithm in mac inference

* removed useless doctest for AC4 in Sudoku because AC4's tests are already present in test_csp.py

* added map coloring SAT problems

* fixed typo errors and removed unnecessary brackets

* reformulated the map coloring problem

* Revert "reformulated the map coloring problem"

This reverts commit 20ab0e5afa238a0556e68f173b07ad32d0779d3b.

* Revert "fixed typo errors and removed unnecessary brackets"

This reverts commit f743146c43b28e0525b0f0b332faebc78c15946f.

* Revert "added map coloring SAT problems"

This reverts commit 9e0fa550e85081cf5b92fb6a3418384ab5a9fdfd.

* Revert "removed useless doctest for AC4 in Sudoku because AC4's tests are already present in test_csp.py"

This reverts commit b3cd24c511a82275f5b43c9f176396e6ba05f67e.

* Revert "added doctest in Sudoku for AC4 and and the possibility of choosing the constant propagation algorithm in mac inference"

This reverts commit 6986247481a05f1e558b93b2bf3cdae395f9c4ee.

* Revert "added the mentioned AC4 algorithm for constraint propagation"

This reverts commit 03551fbf2aa3980b915d4b6fefcbc70f24547b03.

* added map coloring SAT problem

* fixed build error

* Revert "added map coloring SAT problem"

This reverts commit 93af259e4811ddd775429f8a334111b9dd9e268c.

* Revert "fixed build error"

This reverts commit 6641c2c861728f3d43d3931ef201c6f7093cbc96.

* added map coloring SAT problem

* removed redundant parentheses

* added Viterbi algorithm