0.6

Fixes:

    superd:
    - Support using environment variables from multiple sources
    - Address several data race conditions and intermittent test failures
    - No longer indicate a 'failed' status being reported when a service is
      stopped and it exists with a non-zero return code

New Features:

    superd:
    - Support for Environment= in .service files (todo #15)
    - Use colors for INFO and DEBUG messages in log
    - Service stdout/stderr) is printed to the log by default, -v is no longer
      required

    superctl:
    - Completion support for zsh