added similar tracks feature

lib/beatport/catalog/track.rb

@@ -43,6 +43,17 @@ def self.most_popular_for_label(id, options = {})
         options[:collection] = true
         Client.retrieve "most-popular/label", Track, options
       end
+
+      # also works for multiple id's as input
+      def self.similar(id, options = {}) 
+        options[:id] = id
+        options[:collection] = true
+        Client.retrieve "tracks/similar", Track, options
+      end
+
+      def similar(options = {})
+        @similar ||= Track.similar(id, options)
+      end
 
     end
   end

spec/catalog/track_spec.rb

@@ -177,6 +177,16 @@ module Beatport::Catalog
         end
       end      
     end
+    describe '.similar' do
+      it "should get a list of tracks similar to track with id 1217790" do
+        tracks = Track.similar 1217790
+        tracks.length.should be > 1
+      end
+      it "should get a list of tracks similar to a list of track ids" do
+        tracks = Track.similar "4166013,1217790"
+        tracks.length.should be > 1
+      end
+    end
   end
 end