[Delete] BufferMessageEvent 移除缓冲消息事件;

[Add] BufferedMessageSender 增加缓冲消息发送器, 用于替代BufferMessageEvent;
[Change] BotCommandProcess 将Random命令中所使用的BufferMessageEvent替换成BufferedMessageSender;

src/main/java/net/lamgc/cgj/bot/event/BufferedMessageSender.java

@@ -0,0 +1,23 @@
+package net.lamgc.cgj.bot.event;
+
+import net.lamgc.cgj.bot.message.MessageSender;
+
+public class BufferedMessageSender implements MessageSender {
+
+    private final StringBuffer buffer = new StringBuffer();
+
+    @Override
+    public int sendMessage(String message) {
+        buffer.append(message);
+        return 0;
+    }
+
+    /**
+     * 从缓冲区中取出消息内容.
+     * @return 返回事件发送的消息内容.
+     */
+    public String getBufferContent() {
+        return buffer.toString();
+    }
+
+}