improvement: set more logger metadata, and reset it after span closes

[zachdaniel]

This tracks things like service_version and service in the logger metadata, and also fixes an issue where logger metadata would persist even after a span for a given service has closed. Now we set it to the logger metadata of the current span after closing a span.

[zachdaniel]

I've merged the changes from #142 in this branch because I needed them in addition to my changes. We should merge that one first.