Bugfixes:

* replaced the alsa output device detection and selection mechanisms
  with those from
  https://github.com/ronalde/mpd-configure/detect-alsa-output-capabilities.sh
  This makes it possible for the user to choose a device when multiple
  devices are available.
* added a `APLAY_LIMIT_FILTER` variable which pre-filters the
  available output devices. The resulting filtered list is the input
  for the rest of the script, including the `APLAY_PREFERRED_FILTER`
  filter which still works
* incorporated the contents of the `mpdconfigure-*` files in to the main
  script, which were sourced in earlier versions
* removed the volume control functions because they didn't work
  properly and didn't fit in the scripts typical usage
reflected changes in commit:cb6d162ca4d48222b48c77414076f56ccb8062ae
Bugfixes:

* added SCRIPT_DIR: needed when script is called from another
  directory
* added ALSA_OUTPUT_DISPLAY: fixes the display of card details in case
  there's only one or USER_PROMPTS is set.
Small fix

* added MPD_MUSICDIR: fixes the case when there's no XDG dirs and no
  music dir specified
Documentation fix

* removed and changed non existing example variables
* changed paths to Debian defaults
* added example of using a command (`HOSTNAME="$(hostname)"`)
Small fixes

* check if the preferences file (`mpd-configure.conf`) is present
  before trying to source it
* simpler messages when done
added latest commits
added sample to .gitignore
added tests/samples/cat-stevens-wild-world-hdtracks-24-192.wav to .gitignore
added tests/samples/cat-stevens-wild-world-hdtracks-24-96.wav to .gitignore
added tests/samples/cat-stevens-wild-world-hdtracks-32-96.wav to .gitignore