This:
* adds a global -v flag for verbosity
* refactors the "printer" package to have a DefaultPrinter and package
functions that call it, similar to net/http's DefaultServeMux
* adds printer tests
* moves current users of Debugf to Printf
* moves most users of the "log" package to use "printer"
* demotes noticably noisy log messages to "Debugf", like "IGNORE"-
and "NO_PURGE"-related messages
* WIP
* Enable PTR records in dnsconfig.js, in BIND provider.
* Rename REVERSE() to REV().
* More accurate PTR target checking
* Document REV()
* Fix broken test
