LogEvent.categoryName -> LogEvent.category
Logger is immutable (no setLevel any more)
Log levels defined in configure call, nowhere else
References to Loggers not retained
Clustered appender, multiprocess appender removed - core handles clusters now
Default category needs to be defined, with appender
connect logger, gelf, smtp, hookio appenders removed from core.
reload configuration removed from core - use 'watchr' or something instead
appenders now only need to provide configure function
log4js.configure now only takes single argument (no options)