This still needs cleanup, but this is a first pass the cleans some
cruft and documents our style (in middleware.md) and makes all the
docs match that style.
* Split response size into normal responses and AXFR|IXFR responses.
* Split out incoming sizes as well in normal and AXFR|IXFRs.
* Add meta qtype to the monitored qtypes.
* Make duration to be exported in milliseconds instead of seconds.
