Previously, appenders could only be added by specifying the filepath
to the appender. This required the appender's path to be specified
either relative to the log4js installation, relative to a NODE_PATH
token, or absolute. This creates a coupling between the log4js
configurer and the log4js installation location, or a coupling between
the log4js configurer and the global NODE_PATH. This commit removes
the coupling by allowing the loading of appenders to be done relative
to the log4js configurer.
