Add missing 'num' implementations on models

Add missing 'num' implementations from the following models:

- `channel::{ChannelType, MessageType}`
- `gateway::GameType`

src/model/channel/message.rs

@@ -617,3 +617,20 @@ enum_number!(
         MemberJoin = 7,
     }
 );
+
+impl MessageType {
+    pub fn num(&self) -> u64 {
+        use self::MessageType::*;
+
+        match *self {
+            Regular => 0,
+            GroupRecipientAddition => 1,
+            GroupRecipientRemoval => 2,
+            GroupCallCreation => 3,
+            GroupNameUpdate => 4,
+            GroupIconUpdate => 5,
+            PinsAdd => 6,
+            MemberJoin => 7,
+        }
+    }
+}

src/model/channel/mod.rs

@@ -570,6 +570,16 @@ impl ChannelType {
             ChannelType::Category => "category",
         }
     }
+
+    pub fn num(&self) -> u64 {
+        match *self {
+            ChannelType::Text => 0,
+            ChannelType::Private => 1,
+            ChannelType::Voice => 2,
+            ChannelType::Group => 3,
+            ChannelType::Category => 4,
+        }
+    }
 }
 
 #[derive(Deserialize)]

src/model/gateway.rs

@@ -192,6 +192,19 @@ enum_number!(
     }
 );
 
+impl GameType {
+    pub fn num(&self) -> u64 {
+        use self::GameType::*;
+
+        match *self {
+            Playing => 0,
+            Streaming => 1,
+            Listening => 2,
+            Watching => 3,
+        }
+    }
+}
+
 impl Default for GameType {
     fn default() -> Self { GameType::Playing }
 }