v0.6.3

A major new feature release, see release announcement.

• Feature: Simplify usage by supporting new default loop.
  (#87 by @clue)

  // old (still supported)
  $process = new React\ChildProcess\Process($command);
  $process->start($loop);
  
  // new (using default loop)
  $process = new React\ChildProcess\Process($command);
  $process->start();