Removal of `.await` proof of concept.

Hi, a couple of weeks ago there was a really interesting discussion about the possibility to remove the .await syntax. The main motivation was to resolve the inconsistencies that async destructors would cause if implemented. Although I do not support the idea of breaking the entire async ecosystem, I would like to be able to opt into this sort of functionality. As a proof of concept I made the crate suspend\_fn, which hosts a couple of macros that enable this implicit await feature.

As I say in the readme of the project. I propose an alternative to the async keyword (in this case suspend), that supports implicit await and implicit async destructor calls, while current async code remains the same.