audio downloader created

- simpler naming throughout (audio-dl, download(), etc)
- removed 'channel' as arg for download()
- moved all youtube-dl options into this file, as we shouldn't be
  mucking around with the user's youtube-dl conf file, if they have one.
- supressed any non-error output, for easier determination of whether
  errors occurred during download.
- added logging
- added doctests

- removed.  all of this was integrated into audio_dl

- removed.  see mention above in audio_dl