async function support

[zaaack]

Throttle/debounce won't work for async functions, hope could work with functions return a promise. Might help: https://github.com/sindresorhus/promise-fun

[BurtHarris]

Certainly makes sense to me, but both decorator are currently deprecated from this package, and will be removed soon.

[jayphelps]

Indeed, but let's keep it open because this is still valid in general for all decorators. I haven't had time to look into why things are different.