This moves the logger interface into the root package and makes the log
subpackage specific to logrus. Also this makes the Logger interface type
also return other Loggers, such that we can completely encapsulate
logrus.Loggers.
This adds the logrus package to facilitate structured logging. Logrus is
encapsulated in the log/ subpackage and currently used in the influx/
subpackage.
Chris Goller
gunnaraasen
Tim Raymond