[feature] new api `this.id('abc') === 'component_instance_id + abc'` to make html have scope.

[xialvjun]

HTML doesn't have a concept of scope, but it do use concept like variable at many where(like <input id="abc"/><label for="abc">abc</label>). We should add scope to html.

Maybe you say "for label, we can wrap input in label", but it changes the html structure, and there are many other scene using html variable like spectre.

So why not add an api this.instance_id or this.generate_id(abc: string) => this.instance_id + '/' + abc or whatever others can make html scope.

[dantman]

reactjs/rfcs#32