* Upgrade the compatible version of Starlette to `0.12.0`.
* This includes support for ASGI 3 (the latest version of the standard).
* It's now possible to use [Starlette's `StreamingResponse`](https://www.starlette.io/responses/#streamingresponse) with iterators, like [file-like](https://docs.python.org/3/glossary.html#term-file-like-object) objects (as those returned by `open()`).