Merge pull request #53 from juju/helper

feat: add Helper method and function to log correct callsite location

Merge pull request #49 from SimonRichardson/inherited-labels

Inherited labels

Merge pull request #48 from cderici/add-logwithlabelsf-JUJU-5552

Add LogWithLabelsf to dynamically add extra labels to a log entry

Merge pull request #47 from wallyworld/add-log-labels

#47

We want to be able to generate log entries with key value labels. We already in loggo have the concept of labels to group logger modules together with a common name. This PR changes that terminology to "tags" and introduces labels as a map of strings which can be attached to logger instances. Each time a logger instance creates a log entry to hand off to the writer, it adds the labels is has to the log entry. 

To add labels to a logger, use the WithLabels() method.

The (now called) tags are included in the labels map with the special key name "logger-tags". This still allows filtering of log entries by tag name like we rely on in places like juju debug-log etc.

Merge pull request #45 from hmlanigan/get-logger-with-labels

#45

Add GetLoggerWithLabels function, missing from original add of labels for loggers.