simple wrapper for youtube-dl w/ example

 - allows simple calling of youtube-dl
 - args for title, artist, and channel are used to form filename
 - yep
 - outputs youtube-dl stdout to file
 - TODO: output youtube-dl stderr to file!
output is controlled by ytdl_handler now

- changes on per-download basis, so no longer a global setting
improved youtube-dl wrapper function

 - better name (call_youtube_dl)
 - added docstrings to function and file
 - captures stdout & stderr, returns True indicating error if there is output in stderr (fixes issue #34)
   - currently these are written to file, but (TODO:) should instead use the log function (see issue #30 and #24)
Unify the two youtube-dl related branched into one

Merge branch 'youtube-dl-config' into ytdl
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
Merge branch 'ytdl' into develop

Conflicts:
	src/install-youtube-dl-conf.sh