The city may incur indebtedness by issuing its negotiable bonds and notes in anticipation of bonds to finance, in whole or in part, any permanent municipal improvement in accordance with procedural and referendum requirements of State law. The total outstanding debt of the city shall not exceed the limitations established by the State Constitution and State laws for cities of the same class as Springfield. Tax levies required to repay principal and interest on general obligation bonds shall not be included within any ad valorem tax limitations.