feat: Add config option redirect_stderr.

Proposed in #282.

configuration.example.ini

@@ -84,7 +84,10 @@ port = 64738
 #pip3_path = venv/bin/pip
 
 # 'logfile': write logs into this file.
+# 'redirect_strerr': capture outputs from stderr and write into the `logfile`,
+#                    useful for capture the exception message when the bot crash.
 #logfile =
+#redirect_strerr = False
 
 #announce_current_music = True
 #allow_other_channel_message = False