Added stats support

Note:
* The `/status` request always 404s because the `host_bytes` field is invalid. We will have to figure out what we're going to do about bytes-transferred-by-host stats.
* The HTTPS regexes are used for the host stats collection -- mostly because both deal only with hostnames.
* The `stats_*.go` files should eventually be in a `stats` sub-package.
* Test coverage for the `stats_` files is very high. But I didn't add tests for the other files I touched.