Adds release fields asin, barcode and quality.

lib/musicbrainz/bindings/release.rb

@@ -9,7 +9,10 @@ module MusicBrainz
           title: (xml.xpath('./title').text rescue nil),
           status: (xml.xpath('./status').text rescue nil),
           country: (xml.xpath('./country').text rescue nil),
-          date: (xml.xpath('./date').text rescue nil)
+          date: (xml.xpath('./date').text rescue nil),
+          asin: (xml.xpath('./asin').text rescue nil),
+          barcode: (xml.xpath('./barcode').text rescue nil),
+          quality: (xml.xpath('./quality').text rescue nil)
         }
         
         formats = (xml.xpath('./medium-list/medium/format') rescue []).map(&:text)

lib/musicbrainz/models/release.rb

@@ -6,7 +6,10 @@ module MusicBrainz
     field :format, String
     field :date, Date
     field :country, String
-
+    field :asin, String
+    field :barcode, String
+    field :quality, String
+    
     def tracks
       @tracks ||= client.load(:release, { id: id, inc: [:recordings, :media], limit: 100 }, {
         binding: :release_tracks,