Syslog support

[fmorency]

Make use of the tracing-syslog repo at https://github.com/max-heller/tracing-syslog

See tokio-rs/tracing#1137 for the whole story.

I tested this using syslog-ng. When the syslog service is not running, messages are still written to the log files and get picked up when the service restarts.

Fixes #101

@hansl this crate is not on crates.io and this PR uses the git repo directly, fixed to a rev. I don't know the author's intention moving forward but we might want to fork this until/if it gets integrated into the tokio tracing ecosystem. WDYT?

Also, this feature is currently not optional. Do you want me to add a --syslog flag to the binaries?

[hansl]

Make the flag --logmode=syslog that way we can have multiple different modes (like json, term).

[hansl]

Let's reach out to @max-heller to see if he'd need a home for that crate (we could have it in liftedinit) or if he's planning to maintain it and publish it soon. It seems simple enough.

[hansl]

LGTM with the change from stdout to stderr

[max-heller]

Let's reach out to @max-heller to see if he'd need a home for that crate (we could have it in liftedinit) or if he's planning to maintain it and publish it soon. It seems simple enough.

Published as syslog-tracing, I was trying to get ownership of the name-squat tracing-syslog but couldn't get in contact with the owner.