Add --pipe option to ssh.

Enables commands such as:

```
  ssh -i ~/.ssh/my_id_rsa `platform ssh --pipe` 'tail -f /var/log/deploy.log'
```
Detect piped output automatically given the posix extension
Merge pull request #152 from pjcdawkins/feature/ssh-pipe-option

Add --pipe option to ssh.
Add auto-completion.

Squashing commits including:

  Add platform.rc file
  Update symfony-console-completion to 0.4.2 and remove custom shell detection.
  Auto-complete project IDs.
  Add auto-completion set-up to the README.md.
  Complete for environment IDs.
  Support PHP 5.3 by removing $this from the closure.
  Suppress API exceptions during autocompletion.
  Autocomplete environments to check out
  Remove unused import after rebase.
  Cleanup after upstream improvements.
Merge pull request #158 from pjcdawkins/feature/auto-completion

Support auto-completion.
Get Composer to find the dev dependency for symfony-console-completion.
Second attempt
Update composer.lock
Third attempt
Updating/installing via 'require' is broken.

Needs a new tagged version of symfony-console-completion. This Composer issue
is the problem: https://github.com/composer/composer/issues/3367
Improve error if the autoload.php is not present.
Test on PHP 5.3
Update console completion dependency, now tagged as stable upstream.
Re-enable exceptions when getting environments.

Need to find some other way to handle exceptions during auto-completion.
Simplify asking confirm questions.
Release v1.3.0
Remove excess semicolons.
drush version -> drush --version

See issue #160
Hide the completion command in the list.
Ignore missing sites/default dir in Drupal toolstack.