Revert "remove macOS support"

This reverts commit 518ce0187a.

doc/mpdconf.example

@@ -337,6 +337,15 @@ input {
 #	mixer_type	"hardware"
 #}
 #
+# An example of an OS X output:
+#
+#audio_output {
+#	type		"osx"
+#	name		"My OS X Device"
+##	device		"Built-in Output"	# optional
+##	channel_map      "-1,-1,0,1"	# optional
+#}
+#
 ## Example "pipe" output:
 #
 #audio_output {