New solver tracker

[tias]

Meta-issue to track issues and PRs about solvers not yet in CPMpy.

Anybody considering adding a solver, this documentation can be helpful: https://cpmpy.readthedocs.io/en/latest/adding_solver.html

With PR:

• SCIP: scip interface (first version) #412 (ILP)
• cvc5: cvc5 SMT solver #784 (SMT)

With discussion:

• PyCSP3: Adding PyCSP3 as a solver #655 (esp for XCSP3 writing)
• Toulbar2: Adding Toulbar 2 #404 (weighted CSP solver, has XCSP3 interface already?)
• MaxHS: short-term solvers to add #148 (MaxSAT, has python interface, not on pip)

Others mentioned in the earlier meta-issue #148: PySMT, Haddock (MDDs)