Automatically create underlying SLF4J logger with name autodetection

This is solution of some issues described here: https://github.com/typesafehub/scalalogging/issues/28
Subclassing from Logging trait can make impossible to configure logging level for some classes, and writing long string like this:

    val log = Logger(LoggerFactory.getLogger(classOf[HereGoesCurrentClassName]))

can be tedious.
With this patch underlying logger name can be detected automatically via macros. All you need to do is:

    val log = Logger()

It finds nearest encircling class and uses its name for creating underlying logger.