Need option to enable shift+click multi-column sorting

[adlaird]

initial proposed structure of this option:

sorting: {
  type: 'multiple' || 'single' (default: 'multiple'),
  modifierActive: true || false (default: true)
}

multiple + true means shift+click will clear sorting and only sort by current column being clicked
single + true means shift+click will keep existing sort and add on current column being clicked

[jonshaffer]

Could we add a property modiferKey: 'shift', even if it only supports on key type in the beginning?