A new law taking effect Saturday is set to dramatically change the way child support is calculated in the state.Illinois for several decades has assessed child support by awarding the custodial parent a certain percentage of the noncustodial parent’s net income based on the number of children to be supported.But on Saturday, Illinois will become the 40th state to adopt what is called the “income-share approach” to child support calculations, where courts will consider both parents’ net income when …