DEBUG (100): Detailed debug information.
INFO (200): Interesting events. Examples: User logs in, SQL logs.
NOTICE (250): Normal but significant events.
WARNING (300): Exceptional occurrences that are not errors. Examples: Use of deprecated APIs, poor use of an API, undesirable things that are not necessarily wrong.
ERROR (400): Runtime errors that do not require immediate action but should typically be logged and monitored.
CRITICAL (500): Critical conditions. Example: Application component unavailable, unexpected exception.
ALERT (550): Action must be taken immediately. Example: Entire website down, database unavailable, etc. This should trigger the SMS alerts and wake you up.
EMERGENCY (600): Emergency: system is unusable.
指定了日志级别，但是貌似得日志记录没啥影响？
怪我咯2017-04-10 15:20:11
我记得在 github 看到过, 如果第二个参数指定的事 Notice, 那么 addDebug 和 addInfo 的 log 会被忽略.
也就是最低错误级别.
