change `in` to `typeof`, which is more understandable and faster according to jsperf
change `in` to `void 0`, which is way faster and consistend with other places where property existence is checked
$.fn.handsontable changes (fix _this = $this notation,  more DRY)
apply(this, ...) seems to be a bug. `instance` shoud be used here. anyway, all code seems to be unaffected
add test for addOnceHook
add missing specs
rename addOnceHook => addHookOnce