+ levels *(LogLevels)*: customizable logging levels
+ The default LogLevels:
* SILENT:-1
* EMERGENCY:0 system is unusable
* ALERT:1 action must be taken immediately
* CRITICAL:2 the system is in critical condition
* ERROR:3 error condition
* WARNING:4 warning condition
* NOTICE:5 a normal but significant condition
* INFO:6 a purely informational message
* DEBUG:7 messages to debug an application
+ level: use the property to get/set the log level.
* defaults to levels.ERROR.
* set 'SILENT' to mute the loglevel msg, it will still print it out if the msg without loglevel.
* setter *(Nubmer|String)*: set the logging level via number or string.
* getter *(String)*: get the logging level string, or get the level number via _level property.
* log()
+ level, name options to context.
+ log(context, args...)