__init__.py -> new --output format + warn if old
__init__.py -> new --output format + warn if old

- Edited __init__.py so that it uses the new {NAME} rather than the old %(NAME)s --output format
- Moved the backwards compatibility code from YoutubeDL.py to __init__.py
- Display a warning if the old format is used
cousteaulecommandant/youtube-dl,cousteaulecommandant/youtube-dl