Use fibers instead of monkey patching

[WyriHaximus]

Depends on: reactphp/async#15

[WyriHaximus]

@SimonFrings @clue @jsor Updated it to the newly released react/async v4. This code is rock solid, been using it in production for over half a year now without any issues.

[clue]

@WyriHaximus Good job! Only briefly eyeballed this, but looks like a major improvement over the previous monkey patching! 👍 Also using similar logic myself to add PSR-15 compatibility for Framework X as discussed in clue/framework-x#185.

[WyriHaximus]

@clue Thanks! It's been a lot easier to use and no more weird bigs due to incompatible code. In the future I hope we can build PSR-15 support directly into react/http when the time is there, but until that we can use this middleware or framework-x to achieve the same. Will tag a release for this tomorrow.