[Filesystem] Initial code for eio-based Filesystem component
Install eio extension on travis
Add ext-eio as require-dev
Anwer all pecl install questions with the default
Merge remote-tracking branch 'origin/master' into filesystem

* origin/master: (190 commits)
  Prepare for v0.2.5 release
  [HttpClient] Call dns properly with promises, use promises internally
  Fix examples in react/dns README
  Add BufferedSink progress events to CHANGELOG
  Add triggering of progress on its promise in BufferedSink
  Add react/promise as a suggestion for react/stream
  Add branch alias for react/dns split
  Changelog date
  Add BufferedSink to CHANGELOG
  Implement BufferedSink which resembles a promise-based async stream_get_contents()
  Move forwardEvents helper method to Util, add tests
  Update react/promise version to 1.0.3
  Add @jsor credit in CHANGELOG
  Fix dns example script
  Add dns-promise to CHANGELOG
  Split first method call in chain to new line
  Move creation of response outside the closure since createStandardResponse() is protected
  Remove unused use statement
  Fix tests
  Fix RetryExecutor
  ...

Conflicts:
	.travis.yml
	composer.lock
Update Filesystem Component

- Use promises instead of callbacks
- Rename Filesystem to LibeioFilesystem
Remove debug statement
Add Filesystem IoException
Improve libeio filesystem tests
Make tests more robusts