This commit brings UCI support to the stubby package.

    o All options are documented in the README.md file.
    o The README.md file has been re-written to include a short usage
      manual.
    o The default configuration now includes more Cloudflare addresses.
    o The stubby service is (re)started using procd triggers from a
      specified interface with a configurable time delay.
    o Round robin use of upstream resolvers is now activated by
      default.
    o Client privacy is now activated by default.
    o Options are added for specifying the log level of the daemon and
      command line options passed to the stubby command.

Signed-off-by: Jonathan G. Underwood <jonathan.underwood@gmail.com>