Parsedmarc

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- Fix base64 attachment decoding (26)

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- Fix crash on empty aggregate report comments (brakhane - 25)
- Add SHA256 hashes of attachments to output
- Add `strip_attachment_payloads` option to functions and
`--strip-attachment-payloads` option to the CLI (23)
- Set `urllib3` version requirements to match `requests`

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- Fix forensic report email processing

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- Fix normalization of the forensic sample from address

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- Fix parsing of some emails
- Fix duplicate forensic report search for Elasticsearch

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- Fix bug where `parsedmarc` would always try to save to Elastic search,
even if only `--hec` was used
- Add options to save reports as a Kafka topic (mikesiegel - 21)
- Major refactoring of functions
- Support parsing forensic reports generated by Brightmail
- Make `sample_headers_only` flag more reliable
- Functions that might be useful to other projects are now stored in
`parsedmarc.utils`:
- `get_base_domain(domain)`
- `get_filename_safe_string(string)`
- `get_ip_address_country(ip_address)`
- `get_ip_address_info(ip_address, nameservers=None, timeout=2.0)`
- `get_reverse_dns(ip_address, nameservers=None, timeout=2.0)`
- `human_timestamp_to_datetime(human_timestamp)`
- `human_timestamp_to_timestamp(human_timestamp)`
- `parse_email(data)`