Why was generators deprecated in favor of async/await?
I got the deprecation warning and was wondering why it was deprecated? 

>koa deprecated Support for generators will be removed in v3. See the documentation for examples of how to convert old middleware https://github.com/koajs/koa/blob/master/docs/migration.md

Was there a specific performance reason? 
A memory allocation issue?
The idea that it would only ever return a single value?

I like async/await just fine. Just curious as to why fully deprecate it and not just let the user choose which style they liked best.  
