v0.6.0

A major feature release with some minor API improvements!
This project now has limited Windows support and supports passing custom pipes
and file descriptors to the child process.

This update involves a few minor BC breaks. We've tried hard to avoid BC breaks
where possible and minimize impact otherwise. We expect that most consumers of
this package will actually not be affected by any BC breaks, see below for more
details.

• Feature / BC break: Support passing custom pipes and file descriptors to child process,
  expose all standard I/O pipes in an array and remove unused Windows-only options.
  (#62, #64 and #65 by @clue)

  BC note: The optional $options parameter in the Process constructor
  has been removed and a new $fds parameter has been added instead. The
  previous $options parameter was Windows-only, available options were not
  documented or referenced anywhere else in this library, so its actual
  impact is expected to be relatively small. See the documentation and the
  following changelog entry if you're looking for Windows support.

• Feature: Support spawning child process on Windows without process I/O pipes.
  (#67 by @clue)

• Feature / BC break: Improve sigchild compatibility and support explicit configuration.
  (#63 by @clue)

  // advanced: not recommended by default
  Process::setSigchildEnabled(true);

  BC note: The old public sigchild methods have been removed, but its
  practical impact is believed to be relatively small due to the automatic detection.

• Improve performance by prefixing all global functions calls with \ to skip
  the look up and resolve process and go straight to the global function.
  (#68 by @WyriHaximus)

• Minor documentation improvements and docblock updates.
  (#59 by @iamluc and #69 by @CharlotteDunois)

• Improve test suite to test against PHP7.2 and PHP 7.3, improve HHVM compatibility,
  add forward compatibility with PHPUnit 7 and run tests on Windows via Travis CI.
  (#66 and #71 by @clue)