-) added support for label (logger categories).

-) added support for label (logger categories): will work together with the following winston pull request: https://github.com/flatiron/winston/pull/326

-) added close() function to allow winston to end the connection to the redis server (taken from https://github.com/Unroll-Me/winston-redis/commit/098fb98fdb39cb7f4ece2d0450475722391aa09e )