Stop doing data-*, aria-*, start using dataSet

The DOM already exposes `data-*` as `dataset` but it's doing transformation from hyphenated to camelCase. [From MDN](https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement.dataset): ``` <div id="user" data-id="1234567890" data-user="johndoe" data-date-of-birth>John Doe </div> var el = document.querySelector('#user'); // el.id == 'user' // el.dataset.id === '1234567890' // el.dataset.user === 'johndoe' // el.dataset.dateOfBirth === '' el.dataset.dateOfBirth = '1960-10-03'; // set the DOB. // 'someDataAttr' in el.dataset === false el.dataset.someDataAttr = 'mydata'; // 'someDataAttr' in el.dataset === true ``` We should just start supporting `dataSet` (because camelCase). This will allow a couple things: - easier reasoning about data attributes (`Object.keys(this.props.dataSet)`) - easier merging (`<div dataSet={merge(this.props.dataSet, {extra: 'value', override: 'value'})} />`) - easier (potentially faster?) updates (just modify `node.dataset`) We'll want to do the reverse of what the DOM is doing. eg `<div dataSet={{dateOfBirth: 'val', foo: 'bar'}} />` becomes `<div data-date-of-birth="val" data-foo="bar"></div>`. To the best of my knowledge, `aria-*` doesn't have a corresponding API, but we should make it work the same way. I think `ariaSet` makes sense.