upmpdcli: an UPnP front-end to the Music Player Daemon

upmpdcli implements an UPnP Media Renderer, using MPD to perform the real
work.

It has been tested with a number of UPnP control points running on an
Android tablet. Audionet and Bubble UPnP work best with it.

How things work: 

The Control Points uses the UPnP protocols to browse the tracks on the
Media Server and choses URIs to be played. It then talks UPnP to umpdcli,
which uses the mpd client protocol to place the URIs into the MPD
playlist. mpd finally retrieves the data from the Media Server using HTTP.


           [UPnP  Control  Point]
            ^                  ^
            |                  |
          (UPnP)             (UPnP)
            |                  |
            V                  |
        [upmpdcli]             |
            ^                  |
            |                  |
      (MPD protocol)           |
            |                  |
            V                  V
          [MPD]<--(HTTP)-->[UPnP Media Server]


Each of the Control point, Media Server, mpd and upmpdcli processes can run
on any network host, there is no reason, for example, for mpd and upmpdcli
to run on the same host.

Install notes: see http://www.lesbonscomptes.com/upmpdcli for now.