Refactor the dmarc_record rule to fix a failing spec.

* Now the dmarc_record rule closely matches the Formal Definition in
  Section 5.3 (https://datatracker.ietf.org/doc/draft-kucherawy-dmarc-base/?include_text=1)
* By using .maybe instead of .repeat, the parse tree is a single Hash
  instead of an Array of Hashes.
Refactor the dmarc_record rule to fix a failing spec.

* Now the dmarc_record rule closely matches the Formal Definition in
  Section 5.3 (https://datatracker.ietf.org/doc/draft-kucherawy-dmarc-base/?include_text=1)
* By using .maybe instead of .repeat, the parse tree is a single Hash
  instead of an Array of Hashes.
Change dmarc_furi to match new dmarc_auri
Merge branch 'parser_refactor' of github.com:trailofbits/dmarc into parser_refactor