v0.8.0

Imported release from original tag date 2022-03-07.

• Feature: Automatically start new fiber for each request on PHP 8.1+.
  (#117 by @clue)

• Feature: Add fiber compatibility mode for PHP < 8.1.
  (#128 by @clue)

• Improve documentation and update installation instructions for react/async.
  (#116 and #126 by @clue and #124, #125 and #127 by @SimonFrings)

• Improve fiber tests to avoid now unneeded await() calls.
  (#118 by @clue)