Add-on for Bro-IDS

This is a simple Add-on which sourcetypes and does index-time field extraction for Bro-IDS logs. Rather than trying to know all the fields in all of the Bro log files, This add-on simply does header field extraction from the "#fields" line in [name].log for any file that matches '/.../bro/logs/*/*', and changes the sourcetype to bro_[name]. This should make this add-on less prone to breaking when the output format of Bro changes, or when log types are added and/or removed. Another benefit is that if log format changes, old and new logs will both continue to have correct fields. The downside to this approach are the same as any index-time field extraction. Index size may be increased and search performance may be reduced, and once the logs are input they are stuck with the fields they came with. Some parts may be inspired by or derived from the Security Onion app by Brad Shoop and TA-Bro by Cedric Le Roux