Use synth address for root server NS

[pinheadmz]

Closes #400

• TODO: Needs tests

Also imports a fix from hnsd PR handshake-org/hnsd#67 which returns empty SOA if _synth is queried by itself (encourages the recursive resolver to ask again with the full synth address)

Third commit adds newlines \n\n before DNS messages in the log. These messages are only printed at --log-level=spam anyway and improve readability a whole heckuva lot:

[coveralls]

Pull Request Test Coverage Report for Build 1283354237

• 15 of 19 (78.95%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 62.207%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/dns/server.js	15	19	78.95%

Files with Coverage Reduction	New Missed Lines	%
lib/protocol/consensus.js	1	82.79%
lib/utils/binary.js	1	56.9%

Totals
Change from base Build 1262200388:	-0.01%
Covered Lines:	21166
Relevant Lines:	31797

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💛 - Coveralls

[buffrr]

I can confirm this PR makes dig +trace usable if hsd is configured as a system resolver. Using a _synth address for the root NS avoids adding an A record to the zone apex 👍

We may want to clean up DNSSEC for _synth negative answers eventually but don't think it's a high priority for now since its mainly for correctness. LGTM.