Use the syslog2 package to correctly send RFC3164 formatted syslog output

[lingfish]

The format that #263 sends isn't technically strict RFC3164; it's more of a raw output, but because it uses Python's SysLogHandler, the PRI is sent, but the HEADER is not.

Merging this in will probably break existing use of this.

Ideally, parsedmarc should also have GELF output, possibly rename the existing feature from #263 to some more like "Raw", and implement this PR.

[seanthegeek]

Yeah, so many people use this project for such a variety of different use cases that I'd rather not break existing functionality. Similar to why I want to be so careful about what I and others do to address #503.

Please update this PR to:

• Address the code style issue
• Add the syslog2 to the dependencies list in pyproject.toml
• Add a format option under the syslog configuration group, with the current raw format being the implicit default, and rfc3164 using syslog2
• Add details about the configuration options to the documentation, and set format = rfc3164 in the example configuration file

[lingfish]

Yeah, all fair points, I kinda mangled this one, and I don't think that syslog2 dep is a good one.. the author has weirdly put debug statements throughout it using print(). I shall work on it.

[lingfish]

I'm aborting this PR in favour of implementing GELF logging instead.