v1.2.0

A major new feature release, see release announcement.

• Feature: Introduce new concept of default loop with the new Loop class.
  (#226 by @WyriHaximus, #229, #231 and #232 by @clue)

  The Loop class exists as a convenient global accessor for the event loop.
  It provides all methods that exist on the LoopInterface as static methods and
  will automatically execute the loop at the end of the program:

  $timer = Loop::addPeriodicTimer(0.1, function () {
      echo 'Tick' . PHP_EOL;
  });
  
  Loop::addTimer(1.0, function () use ($timer) {
      Loop::cancelTimer($timer);
      echo 'Done' . PHP_EOL;
  });

  The explicit loop instructions are still valid and may still be useful in some applications,
  especially for a transition period towards the more concise style.
  The Loop::get() method can be used to get the currently active event loop instance.

  // deprecated
  $loop = React\EventLoop\Factory::create();
  
  // new
  $loop = React\EventLoop\Loop::get();

• Minor documentation improvements and mark legacy extensions as deprecated.
  (#234 by @SimonFrings, #214 by @WyriHaximus and #233 and #235 by @nhedger)

• Improve test suite, use GitHub actions for continuous integration (CI),
  update PHPUnit config and run tests on PHP 8.
  (#212 and #215 by @SimonFrings and #230 by @clue)