fix(source): HLS would not work if used directly.

[Erk-]

This changes HlsRequest to return true in
Compose::should_create_async.

This would otherwise cause it to be spawned on a thread without a
executor causing it to panic.

This would only cause issues if used directly since we otherwise use
Compose::create in a context where we have access to the executor.

Closes #257

Open questions:

• Should the create implementation be removed or have a note that it will panic if called outside of a tokio executor?

[Erk-]

The fails in the tests seems to be that beta and nightly catches more examples of missing documentation and is not caused by this patch.

[FelixMcFelix]

Looks good to me, thanks for figuring this out. Yeah, CI failures are down to a change in how a lint is applied.

[FelixMcFelix]

* [ ]  Should the `create` implementation be removed or have a note that it will panic if called outside of a tokio executor?

I think a note indicating the panic would be most useful here. It is still feasible to call, so it doesn't violate the existing API contract but it's better to not surprise users where possible!

[Erk-]

I added a note about it on the struct

[FelixMcFelix]

Thanks for the fix; feel free to merge when you're ready (I believe you have access?).