add ability to prefix log lines with a.. prefix.

[jonphilpott]

No description provided.

[film42]

prefix.to_s will work here since nil.to_s #=> "".

[film42]

This might actually be a bit problematic since the expectation is that the output is a pure json blob without any formatting or parsing required.

[jonphilpott]

the idea we were discussing was that prefixing the blob with a prefix would allow us to positively identify logstasher output in a stdout stream without having to fully parse the json

[film42]

Won't this break logstash filters that try to parse a json payload?

    filter {
      json {
        source => "message"
      }
    }

[jonphilpott]

if someone defines a prefix then the logstash pipeline will extract the json string after the prefix to a field and then json parse on that new field.