Defines a platform-neutral API for writing log messages.
_Important! By default, no log writer function is registered,
and so nothing is logged. Read on to learn how to properly
configure logging for your application_
## Adding logging to your module
Log messages are written to a [[Logger]]. A canonical
`Logger` instance for a package or module may be obtained
by calling [[logger]].
Logger log = logger(`module hello`);
The methods [[Logger.fatal]], [[Logger.error]],
[[Logger.warn]], ...
