output/shout: rename "encoding" to "encoder"

The user manual specifies "encoder", which is consistent with other
output plugins.  "encoding" should be deprecated.

NEWS

@@ -3,6 +3,8 @@ ver 0.19.18 (not yet released)
   - ffmpeg: fix crash with older FFmpeg versions (< 3.0)
   - ffmpeg: log detailed error message
   - ffmpeg: support FFmpeg 3.1
+* output
+  - shout: recognize setting "encoder" instead of "encoding"
 * require gcc 4.7 or newer
 
 ver 0.19.17 (2016/07/09)

doc/mpdconf.example

@@ -231,7 +231,7 @@ input {
 #
 #audio_output {
 #	type		"shout"
-#	encoding	"ogg"			# optional
+#	encoder		"vorbis"		# optional
 #	name		"My Shout Stream"
 #	host		"localhost"
 #	port		"8000"

src/output/plugins/ShoutOutputPlugin.cxx

@@ -164,7 +164,9 @@ ShoutOutput::Configure(const config_param &param, Error &error)
 		}
 	}
 
-	const char *encoding = param.GetBlockValue("encoding", "ogg");
+	const char *encoding = param.GetBlockValue("encoder", nullptr);
+	if (encoding == nullptr)
+		encoding = param.GetBlockValue("encoding", "vorbis");
 	const auto encoder_plugin = shout_encoder_plugin_get(encoding);
 	if (encoder_plugin == nullptr) {
 		error.Format(config_domain,