Add module to inspect DMARC policies

[colin-stubbs]

Description

Checks for and parses common DMARC TXT records, e.g. _dmarc.target.domain

DMARC policies may contain email addresses for reporting destinations, typically these are software processed inboxes, but they may also be to individual humans or team inboxes.

Example TXT record:

v=DMARC1; p=reject; fo=1; rua=mailto:dmarc-rua@example.com,mailto:someone@third.party; ruf=mailto:dmarc-ruf@example.com,mailto:someone@target.domain;

I have written a module to do this and will submit a PR shortly.