DKIM ([RFC6376]) implementation
Example: ```rust let res: DKIMResult = cfdkim::verifyemail(&logger, &fromdomain, &parsed_email).await?;
if let Some(err) = &res.error() { error!(logger, "dkim verify fail: {}", err); }
println!("dkim={}", res.with_detail()); ```
The verify_email
arguments are the following:
- logger
: [slog]::Logger
- from_domain
: &str ([RFC5322].From's domain)
- parsed_email
: [mailparse]::ParsedMail
Work in progress.