It is the intent of the legislative assembly to simplify the state income tax laws and to demonstrate that federal legislation is not necessary to deal with certain interstate tax problems, by adopting the federal definition of taxable income as the starting point for the computation of state income tax by all taxpayers and providing the necessary adjustments thereto to substantially preserve and maintain existing exemptions and deductions. It is the further intent of the legislative assembly to eliminate double taxation of the earnings of small corporations by recognizing a subchapter S election when made for federal income tax purposes.