add PremiumTier flag, add Guild description property

src/Discord.Net.Core/Entities/Guilds/PremiumTier.cs

@@ -0,0 +1,22 @@
+namespace Discord
+{
+    public enum PremiumTier
+    {
+        /// <summary>
+        ///     Used for guilds that have no guild boosts.
+        /// </summary>
+        None = 0,
+        /// <summary>
+        ///     Used for guilds that have Tier 1 guild boosts.
+        /// </summary>
+        Tier1 = 1,
+        /// <summary>
+        ///     Used for guilds that have Tier 1 guild boosts.
+        /// </summary>
+        Tier2 = 2,
+        /// <summary>
+        ///     Used for guilds that have Tier 1 guild boosts.
+        /// </summary>
+        Tier3 = 3
+    }
+}

src/Discord.Net.Rest/API/Common/Guild.cs

@@ -46,11 +46,13 @@ namespace Discord.API
         [JsonProperty("system_channel_id")]
         public ulong? SystemChannelId { get; set; }
         [JsonProperty("premium_tier")]
-        public int PremiumTier { get; set; }
+        public PremiumTier PremiumTier { get; set; }
         [JsonProperty("vanity_url_code")]
         public string VanityURLCode { get; set; }
+        [JsonProperty("description")]
+        public string Description { get; set; }
         // this value is inverted, flags set will turn OFF features
         [JsonProperty("system_channel_flags")]
-        public int SystemChannelFlags { get; set; }
+        public SystemChannelMessageDeny SystemChannelFlags { get; set; }
     }
 }