Allow Constraint list to be accessed

src/main/java/no/birkett/kiwi/Solver.java

@@ -38,6 +38,9 @@ public class Solver {
     private Row objective = new Row();
     private Row artificial;
 
+    public Set<Constraint> getConstraints() {
+        return cns.keySet();
+    }
 
     /**
      * Add a constraint to the solver.