Add Slack support

vendor/github.com/nlopes/slack/websocket_dm.go

@@ -0,0 +1,23 @@
+package slack
+
+// IMCreatedEvent represents the IM created event
+type IMCreatedEvent struct {
+	Type    string             `json:"type"`
+	User    string             `json:"user"`
+	Channel ChannelCreatedInfo `json:"channel"`
+}
+
+// IMHistoryChangedEvent represents the IM history changed event
+type IMHistoryChangedEvent ChannelHistoryChangedEvent
+
+// IMOpenEvent represents the IM open event
+type IMOpenEvent ChannelInfoEvent
+
+// IMCloseEvent represents the IM close event
+type IMCloseEvent ChannelInfoEvent
+
+// IMMarkedEvent represents the IM marked event
+type IMMarkedEvent ChannelInfoEvent
+
+// IMMarkedHistoryChanged represents the IM marked history changed event
+type IMMarkedHistoryChanged ChannelInfoEvent