DOMTokenList `add` and `contains` methods implemented for `classes` object.
Bug with selector-built instances was fixed.
`classes` object copying done.
`DOMTokenList` `remove` method is implemented for `classes` object.
`DOMTokenList` `toggle` method is implemented for `classes` object.
`updateItems` method is added for `classes` object to allow accessing classes through subscript.
`splice` method was added.
Readme is extended with classList-based functionality presentation