Add elements support

[mrozbarry]

It is a pain to re-type a set of elements if they are being used frequently, ie:

bem = new Bemmer({block: 'my-block'})

MyComponent className: bem.with({element: 'my-component'}),
  MySubComponent className: bem.with({element: 'my-component-child'})
  MySubComponent2 className: bem.with({element: 'my-component-child2'})

Why not allow the following syntax?

bem = new Bemmer({block: 'my-block'})
elems = ['my-component']

MyComponent className: bem.with({elements: elems}),
  MySubComponent className: bem.with({elements: elems.concat('child')})
  MySubComponent2 className: bem.with({elements: elems.concat('child2')})

With heavier nesting in a single component, this syntax could considerably reduce complexity, while sacrificing some readability.

Would this feature be useful to anyone?