add reply and application_command types

discord/enums.py

@@ -178,6 +178,8 @@ class MessageType(Enum):
     guild_discovery_requalified                  = 15
     guild_discovery_grace_period_initial_warning = 16
     guild_discovery_grace_period_final_warning   = 17
+    reply                                        = 19
+    application_command                          = 20
 
 class VoiceRegion(Enum):
     us_west       = 'us-west'

docs/api.rst

@@ -1070,6 +1070,16 @@ of :class:`enum.Enum`.
         Discovery requirements for 3 weeks in a row.
 
         .. versionadded:: 1.7
+    .. attribute:: reply
+
+        The message type denoting that the author is replying to a message.
+
+        .. versionadded:: 2.0
+    .. attribute:: application_command
+
+        The system message denoting that an application (or "slash") command was executed.
+
+        .. versionadded:: 2.0
 
 .. class:: ActivityType