Any city, incorporated town or village of the state, whether organized under the general laws of this state or by special charter or by constitutional charter, by vote of the constitutionally required percentage of the electors thereof voting thereon, may become indebted in an amount exceeding in any year the income and revenue provided for such year plus any unencumbered balances from previous years for any purpose authorized in the charter of such city, incorporated town or village, or by any general law of this state. Such indebtedness shall not exceed five percent of the value of taxable tangible property therein as shown by the last completed assessment for state and county purposes.