Adding more metadata to forward logs

[DrPyser]

Hi!
Thanks for this plugin, my team is using it as part of our logging pipeline

I was wondering if there was a way to add more metadata to log records before sending them to fluentd?
For example, container labels, or any container/service/stack/node information available from the API.
Currently, only timestamp, log, container_id and container_name fields seem to be included.
Maybe this is something that can be addressed "upstream" in the logspout project directly?
I've created an issue there too: gliderlabs/logspout#483.

If doing so would require modifying the code, I'm open to trying my hands at it eventually(I haven't coded in go yet, but it seems like a nice language), and submitting a PR, if I can get some pointers on what would need to be done.

Thanks again!