Require TLS to NATS bus, support custom fields, and more

New features/improvements

• To work against newer bosh directors, this release supports TLS mutual cert authentication to the source NATS server
• Supports custom message fields via -extraFields argument, similar to firehose-to-syslog
• Halts when connection to NATS server is lost. Previously idled with no attempts to reconnect. This behavior parallels firehose-to-syslog and shifts restart/reconnect duties to parent container orchestration
• Allows preventing messages from going to stdout (and thus duplicated by another log stream) via -noNatsMessagesToDebug argument

Limitations

• At present it also requires mutual cert auth to NATS server