Support "media role" property for PulseAudio devices

Support "media role" property for PulseAudio devices

With PulseAudio a client can set various properties to tell the server
more about the client.  One of these properties is a "media role" which
tells the PulseAudio server what type of media the client is supplying.
For example a mp3 player might set a role of "music", or a movie player
might set a role of "video".

You can't do anything in SXEmacs with roles other than set them, but in
your PulseAudio config you can then do nifty things based on them.  Like,
you can get PulseAudio to mute (cork) your "music" streams when you play a
"video" stream.

This changeset allows the user to set the media role via the `:role'
keyword in #'make-audio-device.

	* src/media/sound-pulse.c (sound_pulse_data_s): Add new object,
	`role'.

	* src/media/sound-pulse.c (sound_pulse_create): Parse :role as
	well.

	* src/media/sound-pulse.c (sound_pulse_finish):

	* src/media/sound-pulse.c (sound_pulse_init_mainloop): Set
	PULSE_PROP_media.role with the role.

	* src/media/sound.c (Fmake_audio_device): Document PulseAudio
	roles.

Signed-off-by: Steve Youngs <steve@sxemacs.org>