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.