Fix compiler warnings.
Adjust content of event sent to Riemann:

- `state` is now the `level` of the log event instead of being hard-coded to `error`
- the `logger` of the log event is included in the Riemann event
- the `message` of the log event is included as the `description` of the Riemann event rather than the `message` (`description` is part of the Riemann event schema)
- the `marker` of the log event is added as a `tag` of the Riemann event
- all of the properties of the log event's MDC are added as custom attributes of the Riemann event
Ensure the stacktrace goes to the same place as the error message when something bad happens.
Only add tags if the log event has a marker.
Remove some superfluous comments
Change handling of the `:stacktrace` in the Riemann event:
- only include a `:stacktrace` if the log event includes an  exception
- prepend the exception type and message to the stacktrace as the first line
- indent all subsequent lines with a tab
Tidy up several warnings in SimpleUdpTransport
Ignore IntelliJ project files