Add some docs about normalize.Host and normalize.Name. They are used
correctly in the middleware even though they are somewhat confusing,
esp when you copy from ServerBlockKeys in your middleware.
* add hosts middleware
* forgot pointer receiver
* add appropriately modified hostsfile tests from golang repo
* remove test artifacts, separate hostsfile parsing from caching and opening, remove unused metrics references, move middleware up the chain
* refactored the logic for creating records and filtering ip address versions. also got PTR lookups working
* Add README.md. Modify config to be more concise. Add zones list to config. Filter PTR responses based on zones list.
* add Fallthrough and return correct dns response code otherwise
* Simplified Hostsfile to only store hosts in the zones we care about, and by ip version. Added handler tests and improved other tests.
* oops, goimports loaded a package from a different repo
