function roundNumber (value, decimals = 0) {
  if (!isInteger(decimals) || decimals < 0 || decimals > 15) {
    throw new Error('Number of decimals in function round must be an integer from 0 to 15 inclusive')
  }
  return parseFloat(toFixed(value, decimals))
}
round a number to the given number of decimals, or to zero if decimals is
not provided
@param {number} value
@param {number} decimals       number of decimals, between 0 and 15 (0 by default)
@return {number} roundedValue