Declarative plus check.
Updated README.
Implement random set strategy with the library's framework.
Minor refactor.
Set variable cardinality is now stored in a integer variable. Easier to optimize.
Fixed intermediate variables for the sum operator not being unique.
Fixed full propagation for PropIntChannel.
Minor refactor.
Declaritive IR tests.
Merge branch 'declarative-tests' into develop
Port to newer strategy factory.
Minor refactor.
Removed obsolete test code.