Add hook to allow programmers to defer rendering until styles have been flushed to the DOM

[benduran]

It is possible to have your components rendered more quickly than the styles, which can result in quick flashes of unstyled components before the DOM writes are flushed.

[benduran]

This is no longer the case. A developer can either have the library render immediately (by default), or the developer can defer the rendering by manually grabbing the sheets in the sheet cache and writing them to the DOM themselves. Closing ticket