fix: allow multiple values for tag "musicbrainz-artistid" & "musicbrainz-albumartistid"

issue #2

src/tag.rs

@@ -0,0 +1,45 @@
+use glib::Value;
+use gstreamer::{
+	tags::{merge_strings_with_comma, CustomTag},
+	Tag, TagFlag,
+};
+
+pub struct MbArtistId;
+
+impl<'a> Tag<'a> for MbArtistId {
+	type TagType = &'a str;
+
+	fn tag_name<'b>() -> &'b str {
+		"musicbrainz-artistid"
+	}
+}
+
+impl CustomTag<'_> for MbArtistId {
+	const FLAG: TagFlag = TagFlag::Meta;
+	const NICK: &'static str = "artist ID";
+	const DESCRIPTION: &'static str = "MusicBrainz artist ID";
+
+	fn merge_func(src: &Value) -> Value {
+		merge_strings_with_comma(src)
+	}
+}
+
+pub struct MbAlbumArtistId;
+
+impl<'a> Tag<'a> for MbAlbumArtistId {
+	type TagType = &'a str;
+
+	fn tag_name<'b>() -> &'b str {
+		"musicbrainz-albumartistid"
+	}
+}
+
+impl CustomTag<'_> for MbAlbumArtistId {
+	const FLAG: TagFlag = TagFlag::Meta;
+	const NICK: &'static str = "album artist ID";
+	const DESCRIPTION: &'static str = "MusicBrainz album artist ID";
+
+	fn merge_func(src: &Value) -> Value {
+		merge_strings_with_comma(src)
+	}
+}