Adds Record.SetMessagef to DRY up a bit.
Log is now also a Sink
Re-implement Filter as Info

We don't actually needs filtering. Just needs some ways to add info automatically.
Reduce FilterSync to only perform a level filter.
Remove the Filter concept entirely.
Adds test for merging nil records.
Remove logger impl, need re-think.
Change generic Merge method to just TemplateMerge for merging in templates.
Finish RecordBuilder impl/tests except Child() which requires Logger.
Skeleton for new logger.
Adds a Record.SetIfNot for convenience during record merges.
Minor edit.
Proper ctors for the logger.
Properly creates child logger from record builder.
Logger now actually writes serialized record.